diff --git a/fastpay_core/src/authority.rs b/fastpay_core/src/authority.rs
index f3785f142722d..d0df24b74cff7 100644
--- a/fastpay_core/src/authority.rs
+++ b/fastpay_core/src/authority.rs
@@ -114,8 +114,9 @@ impl AuthorityState {
                 FastPayError::IncorrectSigner
             );
 
+            // The last object in input_objects is always the gas payment object.
+            // TODO: Add get_gas_object_ref() to Order once Transfer order also has gas object.
             if idx + 1 == input_object_cnt {
-                // The last object in input_objects is always the gas payment object.
                 check_gas_requirement(&order, &object)?;
             }
 
@@ -211,7 +212,7 @@ impl AuthorityState {
                     c.type_arguments,
                     inputs,
                     c.pure_arguments,
-                    Some(c.gas_budget),
+                    c.gas_budget,
                     gas_object,
                     tx_ctx,
                 ) {
diff --git a/fastpay_core/src/authority/temporary_store.rs b/fastpay_core/src/authority/temporary_store.rs
index 583cc6e4feb32..5c04b2b5c0c5f 100644
--- a/fastpay_core/src/authority/temporary_store.rs
+++ b/fastpay_core/src/authority/temporary_store.rs
@@ -75,6 +75,19 @@ impl AuthorityTemporaryStore {
             },
             "Object both written and deleted."
         );
+
+        // Check all mutable inputs are either written or deleted
+        debug_assert!(
+            {
+                use std::collections::HashSet;
+                let mut used = HashSet::new();
+                self.written.iter().all(|elt| used.insert(elt.0));
+                self.deleted.iter().all(|elt| used.insert(elt.0));
+
+                self.active_inputs.iter().all(|elt| !used.insert(elt.0))
+            },
+            "Mutable input neither written nor deleted."
+        );
     }
 }
 
diff --git a/fastpay_core/src/unit_tests/authority_tests.rs b/fastpay_core/src/unit_tests/authority_tests.rs
index 29c75d3f6cdb7..fce153d20b63c 100644
--- a/fastpay_core/src/unit_tests/authority_tests.rs
+++ b/fastpay_core/src/unit_tests/authority_tests.rs
@@ -7,7 +7,7 @@ use fastx_adapter::genesis;
 #[cfg(test)]
 use fastx_types::{
     base_types::dbg_addr,
-    gas::{calculate_module_publish_gas, get_gas_balance},
+    gas::{calculate_module_publish_cost, get_gas_balance},
 };
 use move_binary_format::{
     file_format::{self, AddressIdentifierIndex, IdentifierIndex, ModuleHandle},
@@ -199,6 +199,7 @@ fn make_dependent_module(m: &CompiledModule) -> CompiledModule {
     dependent_module
 }
 
+#[cfg(test)]
 fn check_gas_object(
     gas_object: &Object,
     expected_balance: u64,
@@ -262,7 +263,7 @@ async fn test_publish_module_no_dependencies_ok() {
     let mut module_bytes = Vec::new();
     module.serialize(&mut module_bytes).unwrap();
     let module_bytes = vec![module_bytes];
-    let gas_cost = calculate_module_publish_gas(&module_bytes);
+    let gas_cost = calculate_module_publish_cost(&module_bytes);
     let order = Order::new_module(sender, gas_payment_object_ref, module_bytes, &sender_key);
     let module_object_id = TxContext::new(order.digest()).fresh_id();
     let response = send_and_confirm_order(&mut authority, order).await.unwrap();
@@ -319,7 +320,7 @@ async fn test_handle_move_order() {
     let mut genesis_module_objects = genesis.objects.clone();
     let module_object_ref = genesis_module_objects
         .iter()
-        .find_map(|o| match o.data.as_module() {
+        .find_map(|o| match o.data.try_as_module() {
             Some(m) => {
                 if m.self_id().name() == ident_str!("ObjectBasics") {
                     Some((*m.self_id().address(), SequenceNumber::new()))
@@ -350,7 +351,7 @@ async fn test_handle_move_order() {
         MAX_GAS,
         &sender_key,
     );
-    let gas_cost = 142;
+    let gas_cost = 142 + 24; // 142 is for bytecode execution, 24 is for object creation.
     let res = send_and_confirm_order(&mut authority_state, order)
         .await
         .unwrap();
@@ -392,7 +393,7 @@ async fn test_handle_move_order_insufficient_budget() {
     let mut genesis_module_objects = genesis.objects.clone();
     let module_object_ref = genesis_module_objects
         .iter()
-        .find_map(|o| match o.data.as_module() {
+        .find_map(|o| match o.data.try_as_module() {
             Some(m) if m.self_id().name() == ident_str!("ObjectBasics") => {
                 Some((*m.self_id().address(), SequenceNumber::new()))
             }
diff --git a/fastx_programmability/adapter/src/adapter.rs b/fastx_programmability/adapter/src/adapter.rs
index bdb01d90014f9..7c7cf3414cc13 100644
--- a/fastx_programmability/adapter/src/adapter.rs
+++ b/fastx_programmability/adapter/src/adapter.rs
@@ -10,7 +10,10 @@ use fastx_types::{
         TX_CONTEXT_MODULE_NAME, TX_CONTEXT_STRUCT_NAME,
     },
     error::{FastPayError, FastPayResult},
-    gas::{calculate_module_publish_gas, deduct_gas},
+    gas::{
+        calculate_module_publish_cost, calculate_object_creation_cost,
+        calculate_object_deletion_refund, deduct_gas,
+    },
     object::{Data, MoveObject, Object},
     storage::Storage,
 };
@@ -47,8 +50,8 @@ pub fn execute<E: Debug, S: ResourceResolver<Error = E> + ModuleResolver<Error =
     type_args: Vec<TypeTag>,
     object_args: Vec<Object>,
     pure_args: Vec<Vec<u8>>,
-    gas_budget: Option<u64>,
-    gas_object: Object,
+    gas_budget: u64,
+    mut gas_object: Object,
     ctx: TxContext,
 ) -> Result<(), FastPayError> {
     let TypeCheckSuccess {
@@ -69,7 +72,7 @@ pub fn execute<E: Debug, S: ResourceResolver<Error = E> + ModuleResolver<Error =
         .expect("VM creation only fails if natives are invalid, and we created the natives");
     // TODO: Update Move gas constants to reflect the gas fee on fastx.
     let mut gas_status =
-        get_gas_status(gas_budget).map_err(|e| FastPayError::GasBudgetTooHigh {
+        get_gas_status(Some(gas_budget)).map_err(|e| FastPayError::GasBudgetTooHigh {
             error: e.to_string(),
         })?;
     let session = vm.new_session(state_view);
@@ -94,8 +97,6 @@ pub fn execute<E: Debug, S: ResourceResolver<Error = E> + ModuleResolver<Error =
             debug_assert!(change_set.accounts().is_empty());
             // Input ref parameters we put in should be the same number we get out
             debug_assert!(mutable_ref_objects.len() == mutable_ref_values.len());
-            // Either we consumed gas, or budget is not provided hence no gas metering.
-            debug_assert!(gas_used > 0 || gas_budget == None);
             let mutable_refs = mutable_ref_objects
                 .into_iter()
                 .zip(mutable_ref_values.into_iter());
@@ -106,12 +107,20 @@ pub fn execute<E: Debug, S: ResourceResolver<Error = E> + ModuleResolver<Error =
                 events,
                 gas_object,
                 gas_used,
+                gas_budget,
             )?;
             Ok(())
         }
-        ExecutionResult::Fail { error, gas_used: _ } => Err(FastPayError::AbortedExecution {
-            error: error.to_string(),
-        }),
+        ExecutionResult::Fail { error, gas_used } => {
+            // Need to deduct gas even if the execution failed.
+            deduct_gas(&mut gas_object, gas_used as i128)?;
+            state_view.write_object(gas_object);
+            // TODO: Keep track the gas deducted so that we could give them to participants.
+
+            Err(FastPayError::AbortedExecution {
+                error: error.to_string(),
+            })
+        }
     }
 }
 
@@ -127,9 +136,10 @@ pub fn publish<E: Debug, S: ResourceResolver<Error = E> + ModuleResolver<Error =
             error: "Publishing empty list of modules".to_string(),
         });
     }
-    let gas_cost = calculate_module_publish_gas(&module_bytes);
-    deduct_gas(&mut gas_object, gas_cost)?;
+    let gas_cost = calculate_module_publish_cost(&module_bytes);
+    deduct_gas(&mut gas_object, gas_cost as i128)?;
     state_view.write_object(gas_object);
+    // TODO: Keep track the gas deducted so that we could give them to participants.
 
     let mut modules = module_bytes
         .iter()
@@ -217,7 +227,8 @@ fn process_successful_execution<
     mutable_refs: impl Iterator<Item = (Object, Vec<u8>)>,
     events: Vec<Event>,
     mut gas_object: Object,
-    gas_used: u64,
+    mut gas_used: u64,
+    gas_budget: u64,
 ) -> Result<(), FastPayError> {
     for (mut obj, new_contents) in mutable_refs {
         match &mut obj.data {
@@ -259,7 +270,9 @@ fn process_successful_execution<
                         old_object.next_sequence_number = sequence_number;
                         old_object
                     } else {
-                        Object::new_move(move_obj, recipient, SequenceNumber::new())
+                        let obj = Object::new_move(move_obj, recipient, SequenceNumber::new());
+                        gas_used += calculate_object_creation_cost(&obj);
+                        obj
                     };
                     new_object.owner = recipient;
                     state_view.write_object(new_object);
@@ -271,20 +284,29 @@ fn process_successful_execution<
             unimplemented!("Processing user events")
         }
     }
+    if gas_used > gas_budget {
+        return Err(FastPayError::InsufficientGas {
+            error: format!(
+                "Gas budget is {}, not enough to pay for cost {}",
+                gas_budget, gas_used
+            ),
+        });
+    }
     // any object left in `by_value_objects` is an input passed by value that was not transferred or frozen.
     // this means that either the object was (1) deleted from the FastX system altogether, or
     // (2) wrapped inside another object that is in the FastX object pool
     // in either case, we want to delete it
-    for id in by_value_objects.keys() {
+    let mut gas_refund: u64 = 0;
+    for (id, object) in by_value_objects.iter() {
         state_view.delete_object(id);
+        gas_refund += calculate_object_deletion_refund(object);
     }
 
-    if gas_used > 0 {
-        // The fact that Move VM succeeded means that there is enough gas.
-        // Hence deduct_gas cannot fail.
-        deduct_gas(&mut gas_object, gas_used).unwrap();
-        state_view.write_object(gas_object);
-    }
+    // TODO: In the current approach, we basically can use refund gas to pay for current transaction.
+    // Is this allowed?
+    deduct_gas(&mut gas_object, (gas_used as i128) - (gas_refund as i128))?;
+    state_view.write_object(gas_object);
+    // TODO: Keep track the gas deducted so that we could give them to participants.
 
     Ok(())
 }
@@ -392,7 +414,7 @@ fn resolve_and_type_check(
     let mut args = Vec::new();
     let mut mutable_ref_objects = Vec::new();
     let mut by_value_objects = BTreeMap::new();
-    #[allow(unused_mut)]
+    #[cfg(debug_assertions)]
     let mut num_immutable_objects = 0;
     #[cfg(debug_assertions)]
     let num_objects = object_args.len();
diff --git a/fastx_programmability/adapter/src/unit_tests/adapter_tests.rs b/fastx_programmability/adapter/src/unit_tests/adapter_tests.rs
index 84662356c4af4..1ce1ff0d2e758 100644
--- a/fastx_programmability/adapter/src/unit_tests/adapter_tests.rs
+++ b/fastx_programmability/adapter/src/unit_tests/adapter_tests.rs
@@ -40,7 +40,7 @@ impl InMemoryStorage {
     pub fn find_module(&self, name: &str) -> Option<Object> {
         let id = Identifier::new(name).unwrap();
         for o in self.persistent.values() {
-            match o.data.as_module() {
+            match o.data.try_as_module() {
                 Some(m) if m.self_id().name() == id.as_ident_str() => return Some(o.clone()),
                 _ => (),
             }
@@ -126,7 +126,7 @@ fn call(
     native_functions: &NativeFunctionTable,
     name: &str,
     gas_object: Object,
-    gas_budget: Option<u64>,
+    gas_budget: u64,
     object_args: Vec<Object>,
     pure_args: Vec<Vec<u8>>,
 ) -> FastPayResult {
@@ -157,7 +157,11 @@ fn test_object_basics() {
     let mut storage = InMemoryStorage::new(genesis.objects.clone());
 
     // 0. Create a gas object for gas payment. Note that we won't really use it because we won't be providing a gas budget.
-    let gas_object = Object::with_id_for_testing(ObjectID::random());
+    let gas_object = Object::with_id_owner_gas_for_testing(
+        ObjectID::random(),
+        base_types::FastPayAddress::default(),
+        MAX_GAS,
+    );
     storage.write_object(gas_object.clone());
     storage.flush();
 
@@ -175,7 +179,7 @@ fn test_object_basics() {
         &native_functions,
         "create",
         gas_object.clone(),
-        None,
+        MAX_GAS,
         Vec::new(),
         pure_args,
     )
@@ -183,7 +187,7 @@ fn test_object_basics() {
 
     let created = storage.created();
     assert_eq!(created.len(), 1);
-    assert!(storage.updated().is_empty());
+    assert_eq!(storage.updated().len(), 1); // The gas object
     assert!(storage.deleted().is_empty());
     let id1 = created
         .keys()
@@ -204,14 +208,14 @@ fn test_object_basics() {
         &native_functions,
         "transfer",
         gas_object.clone(),
-        None,
+        MAX_GAS,
         vec![obj1.clone()],
         pure_args,
     )
     .unwrap();
 
     let updated = storage.updated();
-    assert_eq!(updated.len(), 1);
+    assert_eq!(updated.len(), 2);
     assert!(storage.created().is_empty());
     assert!(storage.deleted().is_empty());
     storage.flush();
@@ -232,7 +236,7 @@ fn test_object_basics() {
         &native_functions,
         "create",
         gas_object.clone(),
-        None,
+        MAX_GAS,
         Vec::new(),
         pure_args,
     )
@@ -251,13 +255,13 @@ fn test_object_basics() {
         &native_functions,
         "update",
         gas_object.clone(),
-        None,
+        MAX_GAS,
         vec![obj1.clone(), obj2],
         Vec::new(),
     )
     .unwrap();
     let updated = storage.updated();
-    assert_eq!(updated.len(), 1);
+    assert_eq!(updated.len(), 2);
     assert!(storage.created().is_empty());
     assert!(storage.deleted().is_empty());
     storage.flush();
@@ -274,7 +278,7 @@ fn test_object_basics() {
         &native_functions,
         "delete",
         gas_object,
-        None,
+        MAX_GAS,
         vec![obj1],
         Vec::new(),
     )
@@ -282,7 +286,7 @@ fn test_object_basics() {
     let deleted = storage.deleted();
     assert_eq!(deleted.len(), 1);
     assert!(storage.created().is_empty());
-    assert!(storage.updated().is_empty());
+    assert_eq!(storage.updated().len(), 1);
     storage.flush();
     assert!(storage.read_object(&id1).is_none())
 }
@@ -317,7 +321,7 @@ fn test_move_call_insufficient_gas() {
         &native_functions,
         "create",
         gas_object,
-        Some(50), // This budget is not enough to execute all bytecode.
+        50, // This budget is not enough to execute all bytecode.
         Vec::new(),
         pure_args,
     );
diff --git a/fastx_types/src/gas.rs b/fastx_types/src/gas.rs
index 044d599728647..b3f35b6c1fa76 100644
--- a/fastx_types/src/gas.rs
+++ b/fastx_types/src/gas.rs
@@ -29,7 +29,7 @@ pub fn check_gas_requirement(order: &Order, gas_object: &Object) -> FastPayResul
             Ok(())
         }
         OrderKind::Publish(publish) => {
-            assert_eq!(publish.gas_payment.0, gas_object.id());
+            debug_assert_eq!(publish.gas_payment.0, gas_object.id());
             let balance = get_gas_balance(gas_object)?;
             ok_or_gas_error!(
                 balance >= MIN_MOVE_PUBLISH_GAS,
@@ -40,7 +40,7 @@ pub fn check_gas_requirement(order: &Order, gas_object: &Object) -> FastPayResul
             )
         }
         OrderKind::Call(call) => {
-            assert_eq!(call.gas_payment.0, gas_object.id());
+            debug_assert_eq!(call.gas_payment.0, gas_object.id());
             ok_or_gas_error!(
                 call.gas_budget >= MIN_MOVE_CALL_GAS,
                 format!(
@@ -60,15 +60,26 @@ pub fn check_gas_requirement(order: &Order, gas_object: &Object) -> FastPayResul
     }
 }
 
-pub fn deduct_gas(gas_object: &mut Object, amount: u64) -> FastPayResult {
+/// Subtract the gas balance of \p gas_object by \p amount.
+/// \p amount being positive means gas deduction; \p amount being negative
+/// means gas refund.
+pub fn deduct_gas(gas_object: &mut Object, amount: i128) -> FastPayResult {
     let gas_coin = GasCoin::try_from(&*gas_object)?;
-    let balance = gas_coin.value();
+    let balance = gas_coin.value() as i128;
+    let new_balance = balance - amount;
     ok_or_gas_error!(
-        balance >= amount,
+        new_balance >= 0,
         format!("Gas balance is {}, not enough to pay {}", balance, amount)
     )?;
-    let new_gas_coin = GasCoin::new(*gas_coin.id(), balance - amount);
-    gas_object.data.as_move_mut().unwrap().contents = bcs::to_bytes(&new_gas_coin).unwrap();
+    ok_or_gas_error!(
+        new_balance <= u64::MAX as i128,
+        format!(
+            "Gas balance is {}, overflow after reclaiming {}",
+            balance, -amount
+        )
+    )?;
+    let new_gas_coin = GasCoin::new(*gas_coin.id(), new_balance as u64);
+    gas_object.data.try_as_move_mut().unwrap().contents = bcs::to_bytes(&new_gas_coin).unwrap();
     let sequence_number = gas_object.next_sequence_number.increment()?;
     gas_object.next_sequence_number = sequence_number;
     Ok(())
@@ -78,8 +89,18 @@ pub fn get_gas_balance(gas_object: &Object) -> FastPayResult<u64> {
     Ok(GasCoin::try_from(gas_object)?.value())
 }
 
-pub fn calculate_module_publish_gas(module_bytes: &[Vec<u8>]) -> u64 {
+pub fn calculate_module_publish_cost(module_bytes: &[Vec<u8>]) -> u64 {
     // TODO: Figure out module publish gas formula.
     // Currently just use the size in bytes of the modules plus a default minimum.
     module_bytes.iter().map(|v| v.len() as u64).sum::<u64>() + MIN_MOVE_PUBLISH_GAS
 }
+
+pub fn calculate_object_creation_cost(object: &Object) -> u64 {
+    // TODO: Figure out object creation gas formula.
+    object.data.try_as_move().unwrap().contents.len() as u64
+}
+
+pub fn calculate_object_deletion_refund(object: &Object) -> u64 {
+    // TODO: Figure out object creation gas formula.
+    (object.data.try_as_move().unwrap().contents.len() / 2) as u64
+}
diff --git a/fastx_types/src/object.rs b/fastx_types/src/object.rs
index f79693914eade..64f4a25f68f2a 100644
--- a/fastx_types/src/object.rs
+++ b/fastx_types/src/object.rs
@@ -47,7 +47,7 @@ impl Data {
         }
     }
 
-    pub fn as_move(&self) -> Option<&MoveObject> {
+    pub fn try_as_move(&self) -> Option<&MoveObject> {
         use Data::*;
         match self {
             Move(m) => Some(m),
@@ -55,7 +55,7 @@ impl Data {
         }
     }
 
-    pub fn as_move_mut(&mut self) -> Option<&mut MoveObject> {
+    pub fn try_as_move_mut(&mut self) -> Option<&mut MoveObject> {
         use Data::*;
         match self {
             Move(m) => Some(m),
@@ -63,7 +63,7 @@ impl Data {
         }
     }
 
-    pub fn as_module(&self) -> Option<CompiledModule> {
+    pub fn try_as_module(&self) -> Option<CompiledModule> {
         use Data::*;
         match self {
             Move(_) => None,