Futures curves are not flat. When the front month trades below deferred months, the market is in contango; when the front month trades above deferred months, it is in backwardation. This shape determines the roll yield — the gain or loss an investor incurs when rolling an expiring contract into the next one.

Roll yield is separate from spot price moves. A passive long futures position can lose money even if spot prices are flat, purely because of curve shape.

Contango (upward-sloping curve): rolling long positions means selling cheap front and buying expensive back — a negative roll yield.
Backwardation (downward-sloping curve): rolling long positions means selling expensive front and buying cheap back — a positive roll yield.
Curve shape reflects storage costs, convenience yield, and expected supply/demand balances.

Curve Shape	Front vs. Back	Roll Yield (Long)	Typical Driver
Contango	Front < Back	Negative	High storage, ample supply
Backwardation	Front > Back	Positive	Scarcity, high convenience yield