The unexpected costs that arise from having to take/ purchase a large futures position at increasing prices. Therefore, the mark-to-market value of the position jumps up, making it more difficult to exit or offset the position. However, a trader could make profit from a negative slippage if he would be able to create a sufficiently large squeeze. In a negative slippage the price at which a position is taken becomes worse than originally planned or intended.

Generally speaking, negative slippage involves a case where the ask increases in a long position or the bid decreases in a short position.

It is also known as a reverse slippage.