diff --git a/yarn-project/simulator/src/avm/avm_context.test.ts b/yarn-project/simulator/src/avm/avm_context.test.ts
index 01b09d53840..c281f3cf928 100644
--- a/yarn-project/simulator/src/avm/avm_context.test.ts
+++ b/yarn-project/simulator/src/avm/avm_context.test.ts
@@ -9,7 +9,7 @@ describe('Avm Context', () => {
 
     const newAddress = AztecAddress.random();
     const newCalldata = [new Fr(1), new Fr(2)];
-    const allocatedGas = { l1Gas: 1, l2Gas: 2, daGas: 3 };
+    const allocatedGas = { l1Gas: 1, l2Gas: 2, daGas: 3 }; // How much of the current call gas we pass to the nested call
     const newContext = context.createNestedContractCallContext(newAddress, newCalldata, allocatedGas, 'CALL');
 
     expect(newContext.environment).toEqual(
diff --git a/yarn-project/simulator/src/avm/avm_gas.ts b/yarn-project/simulator/src/avm/avm_gas.ts
index 80f30eb0590..c02998f4779 100644
--- a/yarn-project/simulator/src/avm/avm_gas.ts
+++ b/yarn-project/simulator/src/avm/avm_gas.ts
@@ -24,17 +24,20 @@ export function makeGasCost(gasCost: Partial<Gas>) {
   return { ...EmptyGas, ...gasCost };
 }
 
-/** Adds multiple instances of Gas. */
-export function addGas(...gases: Partial<Gas>[]) {
-  return {
-    l1Gas: gases.reduce((acc, gas) => acc + (gas.l1Gas ?? 0), 0),
-    l2Gas: gases.reduce((acc, gas) => acc + (gas.l2Gas ?? 0), 0),
-    daGas: gases.reduce((acc, gas) => acc + (gas.daGas ?? 0), 0),
-  };
+/** Sums together multiple instances of Gas. */
+export function sumGas(...gases: Partial<Gas>[]) {
+  return gases.reduce(
+    (acc: Gas, gas) => ({
+      l1Gas: acc.l1Gas + (gas.l1Gas ?? 0),
+      l2Gas: acc.l2Gas + (gas.l2Gas ?? 0),
+      daGas: acc.daGas + (gas.daGas ?? 0),
+    }),
+    EmptyGas,
+  );
 }
 
 /** Zero gas across all gas dimensions. */
-export const EmptyGas = {
+export const EmptyGas: Gas = {
   l1Gas: 0,
   l2Gas: 0,
   daGas: 0,
diff --git a/yarn-project/simulator/src/avm/opcodes/arithmetic.ts b/yarn-project/simulator/src/avm/opcodes/arithmetic.ts
index e14c779021d..a3186d427cc 100644
--- a/yarn-project/simulator/src/avm/opcodes/arithmetic.ts
+++ b/yarn-project/simulator/src/avm/opcodes/arithmetic.ts
@@ -2,9 +2,9 @@ import type { AvmContext } from '../avm_context.js';
 import {
   type Gas,
   GasCostConstants,
-  addGas,
   getCostFromIndirectAccess,
   getGasCostMultiplierFromTypeTag,
+  sumGas,
 } from '../avm_gas.js';
 import { type Field, type MemoryValue, TypeTag } from '../avm_memory_types.js';
 import { Opcode, OperandType } from '../serialization/instruction_serialization.js';
@@ -29,7 +29,7 @@ export abstract class ThreeOperandArithmeticInstruction extends ThreeOperandInst
       l2Gas: getGasCostMultiplierFromTypeTag(this.inTag) * GasCostConstants.ARITHMETIC_COST_PER_BYTE,
     };
     const indirectCost = getCostFromIndirectAccess(this.indirect);
-    return addGas(arithmeticCost, indirectCost);
+    return sumGas(arithmeticCost, indirectCost);
   }
 
   protected abstract compute(a: MemoryValue, b: MemoryValue): MemoryValue;
diff --git a/yarn-project/simulator/src/avm/opcodes/external_calls.ts b/yarn-project/simulator/src/avm/opcodes/external_calls.ts
index 55f6358a6b2..c02c1ad42db 100644
--- a/yarn-project/simulator/src/avm/opcodes/external_calls.ts
+++ b/yarn-project/simulator/src/avm/opcodes/external_calls.ts
@@ -1,7 +1,7 @@
 import { FunctionSelector } from '@aztec/circuits.js';
 
 import type { AvmContext } from '../avm_context.js';
-import { type Gas, addGas, gasLeftToGas, getCostFromIndirectAccess, getFixedGasCost } from '../avm_gas.js';
+import { type Gas, gasLeftToGas, getCostFromIndirectAccess, getFixedGasCost, sumGas } from '../avm_gas.js';
 import { Field, Uint8 } from '../avm_memory_types.js';
 import { AvmSimulator } from '../avm_simulator.js';
 import { Opcode, OperandType } from '../serialization/instruction_serialization.js';
@@ -49,7 +49,7 @@ abstract class ExternalCall extends Instruction {
 
     const callAddress = context.machineState.memory.getAs<Field>(addrOffset);
     const calldata = context.machineState.memory.getSlice(argsOffset, this.argsSize).map(f => f.toFr());
-    const l1Gas = context.machineState.memory.getAs<Field>(gasOffset).toNumber();
+    const l1Gas = context.machineState.memory.get(gasOffset).toNumber();
     const l2Gas = context.machineState.memory.getAs<Field>(gasOffset + 1).toNumber();
     const daGas = context.machineState.memory.getAs<Field>(gasOffset + 2).toNumber();
     const functionSelector = context.machineState.memory.getAs<Field>(this.temporaryFunctionSelectorOffset).toFr();
@@ -58,7 +58,7 @@ abstract class ExternalCall extends Instruction {
     const baseGas = getFixedGasCost(this.opcode);
     const addressingGasCost = getCostFromIndirectAccess(this.indirect);
     const allocatedGas = { l1Gas, l2Gas, daGas };
-    context.machineState.consumeGas(addGas(baseGas, addressingGasCost, allocatedGas));
+    context.machineState.consumeGas(sumGas(baseGas, addressingGasCost, allocatedGas));
 
     const nestedContext = context.createNestedContractCallContext(
       callAddress.toFr(),
@@ -92,31 +92,35 @@ abstract class ExternalCall extends Instruction {
     context.machineState.incrementPc();
   }
 
-  public get type(): 'CALL' | 'STATICCALL' {
-    const type = super.type;
-    if (type !== 'CALL' && type !== 'STATICCALL') {
-      throw new Error(`Invalid type for ExternalCall instruction: ${type}`);
-    }
-    return type;
-  }
+  public abstract get type(): 'CALL' | 'STATICCALL';
 
   protected execute(_context: AvmContext): Promise<void> {
-    throw new Error(`Unimplemented`);
+    throw new Error(
+      `Instructions with dynamic gas calculation run all logic on the main execute function and do not override the internal execute.`,
+    );
   }
 
   protected gasCost(): Gas {
-    throw new Error(`Unimplemented`);
+    throw new Error(`Instructions with dynamic gas calculation compute gas as part of the main execute function.`);
   }
 }
 
 export class Call extends ExternalCall {
-  static type: string = 'CALL';
+  static type = 'CALL' as const;
   static readonly opcode: Opcode = Opcode.CALL;
+
+  public get type() {
+    return Call.type;
+  }
 }
 
 export class StaticCall extends ExternalCall {
-  static type: string = 'STATICCALL';
+  static type = 'STATICCALL' as const;
   static readonly opcode: Opcode = Opcode.STATICCALL;
+
+  public get type() {
+    return StaticCall.type;
+  }
 }
 
 export class Return extends Instruction {