Zamorak monk bottom

Averages per 1h from the OSRS Wiki. Times in UTC. Bars: trades at the sell price (orange) on top of trades at the buy price (blue).

Buy price: what sellers took when they sold at once (an instant sell), about where a buy offer fills. Sell price: what buyers paid to have one at once (an instant buy), about where a sell offer fills. The gap between them, less tax, is the margin.