This doesn't actually follow. Sitting quietly and doing nothing, you are definitely going to use less gas than you will when moving at all, and unless you spend your entire dive hovering in one place, you are going to be moving.
The bottom line, nannymouse, is efficiency. CO2 production is what determines how much you need to breathe, and the more oxygen you burn, the more CO2 you make. You burn oxygen using muscles, so the less you can DO underwater, the longer your gas will last.
You do less by becoming efficient. That includes streamlining gear, as has already been mentioned. But probably the biggest step toward efficiency is learning to dive in a horizontal position. Why? Because if you are tilted 45 degrees head-up, every time you kick, you're driving yourself upwards. In order not to ascend, you must dive not in neutral buoyancy, but in negative buoyancy, so your tendency to sink counteracts the upward drive from your fins. Now you can see it -- you're wasting half the energy you're putting into kicking to achieve no net propulsion at all!
Getting into a horizontal position is easy, if your gear and weights are properly distributed. Unfortunately, for a lot of people (and especially in cold water) putting all their required weight in the pouches of a weight-integrated BC, or on a weight belt, will almost obligate them to dive in a head-up position. Moving weight up onto your back, either into trim pockets in BCs that have them, or by attaching weights or weight pouches to the cambands of your BC, will make a horizontal position effortless. That is the beginning of efficient diving and better gas consumption.
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