What Is MEV? Maximal Extractable Value Explained

What Is MEV?

MEV stands for Maximal Extractable Value (originally Miner Extractable Value, renamed as Ethereum moved to proof-of-stake). It refers to the profit that can be extracted from a blockchain by participants who have the ability to order, include, or exclude transactions within blocks.

MEV is one of the most important and often misunderstood dynamics in modern DeFi, affecting everything from the prices users receive on DEX swaps to the economics of staking and validator rewards.

This guide explains how MEV works, the main categories of MEV extraction, how the ecosystem has evolved to manage it, and what MEV means for everyday DeFi users.

Why MEV Exists

Blockchains like Ethereum process transactions in blocks, and the entity producing each block (a validator in Ethereum's proof-of-stake system) has significant discretion over which transactions to include and in what order.

Most of the time, validators simply order transactions by gas price (highest first) and include as many as will fit in a block. But for profit-seeking actors, the ability to control transaction ordering creates opportunities to capture value that would otherwise go to other market participants.

Every time a user submits a transaction to a public mempool (the waiting area where pending transactions sit before being included in a block), that transaction becomes visible to sophisticated observers known as searchers.

Searchers analyse pending transactions in real time, identify opportunities to profit from specific transaction orderings, and submit their own transactions (typically with higher priority fees) to exploit those opportunities. This extracted value is MEV.

Common Types of MEV

Arbitrage is the most benign form of MEV. When the same asset trades at different prices on different DEXs, arbitrageurs buy on the cheaper venue and sell on the more expensive one, pocketing the difference. This activity helps maintain price consistency across venues, a socially valuable function and searchers compete to execute these trades quickly.

While arbitrage extracts value from price inefficiencies, it generally does not harm users directly.

Liquidations are another major MEV category. When a lending protocol position falls below its collateralisation threshold, it becomes eligible for liquidation, and liquidators earn a bonus for closing the position and restoring solvency.

Searchers compete to be the first to liquidate eligible positions, and the bonus structure creates meaningful profits.

Like arbitrage, liquidation is socially necessary. Without it, lending protocols would accumulate bad debt - but the competition for liquidation MEV can be intense.

Sandwich attacks are the most infamous form of extractive MEV. When a user submits a large DEX swap to the public mempool, a searcher can see it and execute a front-run/back-run pair:

First, the searcher buys the asset immediately before the user's transaction (pushing the price up), then allows the user's transaction to execute at the inflated price, and finally sells the asset immediately after (capturing profit from the temporary price movement).

The user ends up with worse execution than they would have received otherwise, and the difference is transferred to the searcher.

Long-tail MEV encompasses various more exotic forms, including JIT (just-in-time) liquidity provision on concentrated liquidity DEXs, oracle manipulation attempts, and NFT sniping during price updates. These are more niche but can still represent substantial extraction in specific contexts.

Searchers, Builders, and Validators

The MEV supply chain has become increasingly specialised. Searchers are the entities that identify MEV opportunities and construct transaction bundles (groups of transactions that must execute together) designed to capture that value.

Searchers range from sophisticated quantitative firms running high-frequency infrastructure to individual developers writing arbitrage bots.

Builders are specialised block producers that compete to construct the most profitable possible blocks.

Under Ethereum's current proposer-builder separation (PBS) model, validators do not typically construct their own blocks. Instead, they outsource block construction to builders, who assemble blocks including searcher bundles and other transactions to maximise total extracted value.

Builders pay validators a bid to include their block, and the most profitable block wins.

Validators (block proposers) receive MEV-related payments indirectly through this auction system. Rather than manually searching for MEV opportunities, validators simply select the highest-paying block from competing builders.

This separation of roles is designed to make MEV extraction more competitive and to prevent validator centralisation that might otherwise occur if large staking operations were the only ones capable of capturing MEV.

MEV-Boost and the Flashbots Ecosystem

MEV-Boost is the dominant software infrastructure implementing proposer-builder separation on Ethereum. Developed by the Flashbots team, MEV-Boost allows validators to receive blocks from a marketplace of builders rather than building blocks themselves.

The vast majority of Ethereum validators now run MEV-Boost, creating a standardised MEV auction market.

Flashbots has also built infrastructure for searchers and users. The Flashbots Protect RPC allows users to submit transactions privately (not to the public mempool), which prevents sandwich attacks by hiding transaction details from searchers until the transaction is included in a block.

This private mempool approach has become increasingly popular for DeFi users and is offered by numerous wallets and applications.

Relay services sit between builders and validators, forwarding blocks and ensuring that validators cannot unbundle builder-submitted blocks to steal MEV themselves.

Trust in relays is a current design constraint, users rely on relays to behave honestly, and the relay landscape has evolved as different parties have launched competing relay infrastructure with varying trust assumptions.

How MEV Affects DeFi Users

For typical DeFi users, MEV primarily manifests as worse execution on DEX swaps due to sandwich attacks, failed transactions due to searcher competition, and general slippage that exceeds what would occur in an MEV-free world.

A user swapping $10,000 of ETH for USDC on Uniswap might receive $9,950 worth of USDC instead of $9,980 because a sandwich attack extracted $30 of value from the trade.

The total MEV extracted from Ethereum users has been estimated at hundreds of millions of dollars per year, though the exact figure varies widely by source and methodology. This extraction disproportionately affects larger trades and less sophisticated users who do not take steps to protect themselves.

Users executing small trades generally see less MEV impact because the extraction cost (gas + infrastructure) exceeds the profit from sandwiching.

Protecting against MEV involves several approaches:

• Using private transaction submission (Flashbots Protect, MEV Blocker, and similar RPCs).
• Setting appropriate slippage tolerances, using DEXs and aggregators with built-in MEV protection (CoW Swap, 1inch Fusion, UniswapX).

• Avoiding large trades during high-volatility periods when MEV activity is most intense.

MEV on Other Chains

While Ethereum is where MEV research and infrastructure have developed most extensively, MEV exists on every blockchain that processes transactions in ordered blocks.

Solana has significant MEV activity but a different structure due to its higher throughput and different consensus mechanism. Jito is the leading MEV infrastructure on Solana, analogous to Flashbots on Ethereum.

Other chains (Polygon, BNB Chain, Arbitrum, Optimism, Base) have varying degrees of MEV activity depending on their transaction ordering rules and ecosystem maturity.

Layer 2 rollups introduce additional MEV considerations. Many L2s currently use centralised sequencers that could theoretically extract MEV without the competitive auction mechanisms available on Ethereum mainnet.

The decentralization of L2 sequencing is an active area of research and development, with projects exploring various designs for fair ordering, shared sequencing, and MEV redistribution.

MEV Redistribution and the Future

An increasingly important trend is MEV redistribution, mechanisms that return extracted value to users rather than allowing searchers and validators to capture it all.

Some DEX aggregators now share MEV profits with users by executing swaps through order flow auctions. Backrunning-as-a-service platforms let users share in the MEV generated by their own transactions.

Longer-term research directions include encrypted mempools (where transaction details are hidden from everyone until inclusion), fair ordering protocols (that eliminate certain forms of MEV at the consensus level), and application-specific MEV mitigation (where individual protocols design their mechanics to minimise MEV opportunities).

These are active research areas with no clear winners yet, and the MEV landscape will likely continue evolving significantly over the coming years.

MEV Risks and Considerations

Users interacting with DeFi should understand several MEV-related considerations. Slippage settings matter more than users often realise, setting slippage too high increases vulnerability to sandwich attacks, while setting it too low may cause transactions to fail.

Default slippage values on DEX interfaces are often a reasonable starting point, but users should adjust based on trade size and volatility.

Public mempool submission exposes transactions to searchers. Using a private RPC endpoint reduces this exposure, though it may introduce trust assumptions in the RPC provider. Users should consider the trade-offs when selecting wallet RPC settings.

MEV-aware applications often provide better execution than MEV-unaware alternatives. Aggregators with built-in MEV protection, batch auctions (like CoW Swap), and intent-based trading (1inch Fusion, UniswapX) are designed with MEV dynamics in mind and can deliver better net execution than naive on-chain routing.

Exploring MEV-Aware Trading via Portals.fi

Portals.fi is a DeFi aggregation platform that allows users to interact with various DeFi protocols through a unified interface.

Users exploring MEV-aware trading options can access different execution venues and DeFi opportunities from a single access point.

This article is for informational purposes only and does not constitute financial advice. MEV is a complex topic and the dynamics described here continue to evolve. DeFi trading carries inherent risks including slippage, failed transactions, and smart contract vulnerabilities.

Always conduct your own research before interacting with any protocol. For our full disclaimer, please visit disclaimer.