If the futures price of a commodity investment is lower than the spot price (so-called backwardation), investors can achieve a positive roll yield. In the opposite case (contango), the roll yield is negative.

For example, if the oil price is $100 per barrel and the 1‑month future price is $95 per barrel, an investor can achieve a roll yield of $5 per barrel at a constant spot price: Long (buying the 95$) future. Since the spot price remains constant at 100$ per barrel, the futures price approaches 100$ within one month. The investor can then extend the future by another month (“roll”) with the same expectations.