Fee Structure & Calculations

o2 Exchange uses a transparent fee structure designed to reward liquidity providers and maintain a healthy trading ecosystem.

Fee Types

Trading Fees:

• Maker fees - When you add liquidity to the order book
• Taker fees - When you remove liquidity from the order book
• No hidden fees - What you see is what you pay

How Fees Work

o2 Exchange fees are determined by when your order executes, not by order type or buy/sell direction. This is based on the order book smart contract's storage mechanism.

Fee Type	Maker (0.00% - FREE!)	Taker (0.01%)
What happens	Order stored in contract, waits for match	Order executes in same transaction
Liquidity	Adds liquidity to order book	Removes liquidity from order book
Examples	Limit order below/above spread	Market orders, aggressive limit orders

The Storage Rule

Maker = Stored in contract → 0.00% (FREE)

• Your order is stored in the on-chain order book
• Waits for a future match
• Provides liquidity to other traders

Taker = Executes immediately → 0.01%

• Your order executes in the same transaction it's submitted
• Fills as much as possible against existing orders
• Any unfilled portion automatically becomes a maker order on the book

Key insight: Buy/sell direction doesn't matter. What matters is whether your order enters storage or executes immediately.

Fee Examples & Calculations

Understanding fees is best learned through real examples. Each scenario below shows the complete picture: market conditions, fee allocation between parties, and exact calculations.

Example 1: Market Order (Always Taker)

Scenario: You want to buy $1,000 worth of BTC immediately

Market conditions:

• Best ask: $50,000 per BTC
• Existing limit sell orders in the book at $50,000

Fee allocation:

• You (market buy): Taker → 0.01% fee
• Existing sellers (limit orders in storage): Maker → 0.00% fee

Your calculation:

Order value: $1,000
Your fee (Taker): 0.01% = $1,000 × 0.0001 = $0.10

Total you pay: $1,000 + $0.10 = $1,000.10
BTC you receive: $999.90 ÷ $50,000 = 0.019998 BTC
Effective price: $50,005 per BTC

Key insight: Market orders execute immediately in the same transaction, so they're always takers. The sellers who had orders waiting in storage are makers and pay no fees.

Example 2: Limit Order That Rests (Maker)

Scenario: You want to buy 0.02 BTC but only at $49,500 or better

Market conditions:

• Current best ask: $50,000
• Your limit: $49,500 (below market, won't execute immediately)
• Your order enters on-chain storage

Fee allocation:

• You (limit order in storage): Maker → 0.00% fee
• Future seller who matches your order: Taker → 0.01% fee

When order eventually executes (someone sells to you at $49,500):

BTC quantity: 0.02 BTC
Execution price: $49,500
Gross value: 0.02 × $49,500 = $990.00

Your fee (Maker): 0.00% = $0.00
Seller's fee (Taker): 0.01% = $0.99

Total cost to you: $990.00 + $0.00 = $990.00
Total seller receives: $990.00 - $0.99 = $989.01

Key insight: Your order became a maker because it rested in the order book storage waiting for a match. You saved $0.99 compared to using a market order! If you had placed a limit order at $50,000 or higher, it would have executed immediately as a taker.

Example 3: Two Limit Orders Match (Including Aggressive Limits)

Scenario: Trader A has a buy limit order waiting, Trader B submits a sell limit order that crosses the spread

Market conditions:

• Trader A placed a buy limit order at $50,000 yesterday (in storage)
• Trader B places a sell limit order at $50,000 or lower today
• Trade amount: 0.5 BTC

Fee allocation:

• Trader A (first limit, in storage): Maker → 0.00% fee
• Trader B (second limit, crosses spread): Taker → 0.01% fee

Trader A's outcome (Buyer, Maker):

BTC purchased: 0.5 BTC
Price: $50,000 per BTC
Gross value: $25,000

Fee (Maker): $0.00
Total paid: $25,000.00

Trader B's outcome (Seller, Taker):

BTC sold: 0.5 BTC
Price: $50,000 per BTC
Gross value: $25,000

Fee (Taker): $25,000 × 0.0001 = $2.50
Net received: $24,997.50

Key insight: Both used limit orders, but Trader B's order crossed the spread and executed immediately, making them the taker. First to storage wins maker status—even aggressive limit orders are takers if they execute immediately.

Example 4: Large Order with Partial Fills

Scenario: Sell 1 BTC with market order, executes in multiple parts

Order book state:

Bids (Buyers):
$49,900 - 0.3 BTC
$49,850 - 0.4 BTC  
$49,800 - 0.3 BTC

Execution breakdown:

Fill 1: 0.3 BTC @ $49,900 = $14,970.00
Fill 2: 0.4 BTC @ $49,850 = $19,940.00  
Fill 3: 0.3 BTC @ $49,800 = $14,940.00
Total: 1.0 BTC for $49,850.00 (average price)

Fee calculation:

Total value: $49,850.00
Taker fee (0.01%): $49,850.00 × 0.0001 = $4.985
Net proceeds: $49,850.00 - $4.985 = $49,845.015

Key points:

• One fee calculation on total value (not per fill)
• Average execution price: $49,850
• Total fee: $4.985
• Net received: $49,845.015

Quick Reference

Will I Pay Maker or Taker Fees?

Your Order	Result	Fee	Why?
Market buy or market sell	Always Taker	0.01%	Executes immediately, never stored
Limit buy order below ask	Maker	0.00%	Waits in storage for match
Limit sell order above bid	Maker	0.00%	Waits in storage for match
Limit buy order at or above ask	Taker	0.01%	Crosses spread, executes immediately
Limit sell order at or below bid	Taker	0.01%	Crosses spread, executes immediately

Key Takeaways

1. First to storage wins maker status - Doesn't matter if you're buying or selling
2. Crossing the spread = taker - Even with limit orders
3. One fee per order - Not per partial fill

Fee Comparison

o2 vs Other Exchanges

Exchange	Maker Fee	Taker Fee	Gas Fees
o2 Exchange	0.00%	0.01%	Sponsored
Uniswap V3	0.01-1.00%	0.01-1.00%	User pays
Hyperliquid	0.00-0.01%	0.025-0.035%	User pays