What is Fuel?

Fuel v1 began as a layer-2 (L2) scalability technology for a monolithic Ethereum. It was the first optimistic rollup on mainnet Ethereum, deployed at the end of 2020.

Today, Fuel is the fastest modular execution layer. Fuel delivers the highest security and flexible throughput, with a focus on a superior developer experience.

Here’s how we do it:

Parallel Transaction Execution

Fuel delivers unmatched processing capacity through its ability to execute transactions in parallel by using strict state access lists in the form of a UTXO model. This enables Fuel to use far more threads and cores of your CPU that are typically idle in single-threaded blockchains. As a result, Fuel can deliver far more compute, state accesses, and transactional throughput than its single-threaded counterparts.

With the EVM, it is difficult to know if, and where there are dependencies between transactions, so you are forced to execute transactions sequentially.

The FuelVM uses the UTXO model, enabling parallel transaction execution by identifying transaction dependencies through what is known as state access lists. With the FuelVM, Fuel full nodes identify the accounts that a transaction touches, mapping out dependencies before execution.


The FuelVM learns from the Ethereum ecosystem, implementing improvements that were suggested to the Ethereum VM (EVM) for many years but couldn’t be implemented due to the need to maintain backward compatibility.

Here are some EIP that have been implemented in the FuelVM:

Easy ParallelizabilityAllow transactions in the EVM to be processed in parallel by specifying what addresses they can access.Fuel can execute transactions in parallel by using strict state access lists with our UTXO model. This allows Fuel to use of all the threads and cores of your CPU to validate transactions.
EIP-2098: Compact Signature RepresentationReduce signatures from 65 bytes to 64 bytes to simplify handling transactions in client code, reduce gas costs, and reduce transaction sizes.Fuel compresses signature data by a byte, from 65 to 64 bytes.
EIP-3074: AUTH and AUTHCALL opcodesIntroduces two EVM instructions, AUTH and AUTHCALL, to enable batching capabilities, allowing for gas sponsoring, expirations, scripting, and beyond.Fuel has scripts and predicates that, when combined, allow the execution of multiple calls in a single batch.
EIP-3102: Binary Trie StructureIntroduces binary structure and merkelization rule for the account and storage tries, which are merged into a single “state” trie. Binary tries make for smaller (~4x) proofs than hexary tries, making it the design of choice for a stateless-friendly Ethereum.Fuel uses a binary Sparse Merkle Trie instead of a Patricia Merkle Trie, which makes for smaller proofs and results in better performance.
EIP-4758: Deactivate SELFDESTRUCTRename SELFDESTRUCT opcode to SENDALL, and only immediately move all ETH in the account to the target; no longer destroying code or storage or alters the nonce. Disabling SELFDESTRUCT will be a requirement for statelessness.The FuelVM doesn't have a SELFDESTRUCT opcode which can complicate client implementations.
EIP-5027: Remove the limit on contract code sizeRemove the limit on the code size so that users can deploy a large-code contract without worrying about splitting the contract into several sub-contracts. With the dramatic growth of decentralized applications, the functionalities of smart contracts are becoming more and more complicated, and thus, the sizes of newly developed contracts are steadily increasing. As a result, we are facing more issues with the 24576-bytes contract size limit.FuelVM doesn't have a limit on the size of a single contract below their physical limits. We have an instruction that allows you to load bytecode from another contract into the current execution context, allowing you to use it as a single contract even if you have to split bytecode across multiple transactions. It'll have a single monolithic bytecode and one state. In EVM, if you spit a contract across two transactions, it's two separate contracts, and you have to do things like delegate calls to share the state between the two contracts and can't do things like jump between bytecode on each contract.
EIP-5065: Instruction for Transferring EtherAdd a new instruction that transfers ether to a destination address without handing over the flow of execution to it. Ethereum currently has no ideal way to transfer ether without transferring the execution flow. People have come up with reentrancy guards and similar solutions to prevent some types of attacks, but it’s not an ideal solution.The FuelVM has an instruction called TR, short for transfer, which transfers a native asset to a contract but doesn't allow the receiving contract to execute logic. You might want to do this to ensure the receiving contract cannot reenter. This doesn't exist as a native, first-class instruction in the EVM- you can do this by self-destructing a contract but it's a messy workaround that only works for ETH.
EIP-86: Abstraction of Transaction Origin and Signature and EIP-2938: Account AbstractionImplements a set of changes that serve the combined purpose of “abstracting out” signature verification and nonce checking, allowing users to create “account contracts” that perform any desired signature/nonce checks instead of using the mechanism currently hard-coded into transaction processing.FuelVM has stateless account abstraction, enabling application-layer logic to configure validity rules of transactions. On Ethereum today, a transaction is valid if the user has enough Ether, the nonce is correct, and signature is valid. With account abstraction, the user can change the validity of the transaction logic without a hard fork. This could mean changes to the signature scheme or natively locking an account behind a multisig.
EIP-1051: Overflow Checking for the EVMThis EIP adds overflow checking for EVM arithmetic operations and two new opcodes that check and clear the overflow flags. Since the EVM operates on mod 2^256 integers and provides no built-in overflow detection or prevention, this requires manual checks on every arithmetic operation.Overflow checking is built into the FuelVM and can be optionally disabled.
EIP-2803: Rich TransactionsIf a transaction has a to of address x, then the data of the transaction will be treated as EVM bytecode, and it will be executed from the context of the CALLER of the transaction (aka: the transaction signer). Many Ethereum DApps require users to approve multiple transactions to produce one effect. This results in a poor user experience and complicates the experience of interacting with DApps.The FuelVM has scripts that implement this.
EIP-2926: Chunk-based Code MerkelizationBytecode is currently the second contributor to block witness size after the proof hashes. Transitioning the trie from hexary to binary reduces the hash section of the witness by 3x, thereby making code the first contributor. By breaking contract code into chunks and committing to those chunks in a Merkle tree, stateless clients would only need the chunks that were touched during a given transaction to execute it.To get a code hash on Ethereum, you hash together all the byte code. The problem is that if you want to do things with statelessness or fraud proofs, to show that this hash is valid, you have to provide all the byte code, up to 24KB per contract. This EIP suggests we should merkalize it instead of hashing. The FuelVM implements this by having code roots instead of code hashes.

Sway Language

Sway is a domain-specific language (DSL) for the Fuel Virtual Machine (FuelVM), a blockchain-optimized VM designed for the Fuel blockchain. Sway is based on Rust and includes syntax to leverage a blockchain VM without a needlessly verbose boilerplate.

Sway was created alongside the FuelVM and designed for the high-compute Fuel environment. Check out the Sway docs here.

Developer Tooling

Fuel Labs is developing a suite of developer tooling to create a seamless developer experience. By creating everything in-house, Fuel Labs guarantees the maintenance of the toolchain, avoiding the pitfalls of a fragmented developer ecosystem.

Fuel provides a powerful and sleek developer experience with our own domain-specific language, called Sway, and a supportive toolchain, called Forc (the Fuel Orchestrator). Our development environment retains the benefits of smart contract languages like Solidity, while adopting the paradigms introduced in the Rust tooling ecosystem. Now, developers can have a completely vertically-integrated experience where every component from the virtual machine through to the CLI works in harmony.

The Fuel Toolchain: Forc: build, run tests, launch a local instance of a block explorer, format.

Check out the Fuel Toolchain here.

Coming Soon: A suite of auditing facilities, from fuzzing and formal verification to code coverage and runtime gating.