My van has recently started using an excessive amount of gas.There are no leaks in the line or tank. Causes?

The van is using almost twice as much gas as before. The gas gauge does not work so I always do the calculation and have done this for more than a yr with no problems and now i am constantly running out of gas. I checked EGR valve and it is not sticky. But i could not check with an ohmiter. What could be causing this sudden problem?