All trading on Omen currently uses market orders with a slippage tolerance. Limit orders are not supported at this time, though they are planned for a future release.
This applies to both opening and closing positions. To exit a position, you sell it at the best price currently available on the order book.
Slippage and estimates
Prices come from a live Polymarket order book, so the price shown when you enter an order is an estimate based on the best price currently available. Two things can change the price you actually get:
Order book depth. If there isn't enough size at the best price, the remainder of your order fills at worse prices further down the book.
Market movement. Prices can move between the moment you submit an order and the moment it is matched, particularly during live sports and news events.
The order review window gives you the most accurate estimate available, because at that point we know how much you intend to trade and can calculate against real order book depth. On thin markets, the estimate in the review window can differ substantially from the one in the order entry box. See Trading Markets With Low Liquidity.
Your final fill price and contract count are shown on the confirmation screen after the order is placed.
Order rejection
If the price changes drastically between the time you place your order and the time it is matched, we will reject the order for safety rather than filling it at an unexpected price. Rejected orders do not affect your account balance.
When an event ends
Positions are not automatically sold when an event ends — they are automatically resolved. Once the underlying market officially resolves on Polymarket, each position settles at its final value and moves to your closed positions list. You do not need to do anything.
We strongly recommend against trying to trade a market after it has closed but before it has resolved. Pricing in that window can be inaccurate, and Polymarket imposes additional fees for selling a position rather than waiting for it to resolve. Holding until resolution avoids both. See Trading Fees and Why My Positions, Odds, or Balances Look Wrong.