Can you use 30w engine oil on a 1999 ford contour?

I would not recommend using any single-weight motor oil in any modern car engine. They are designed with much closer tolerances than older engines, and they need the ability of multigrade oils to flow easily when cold to provide proper lubrication quickly when started. Single grade oils are too sluggish, especially in cold weather, to provide this protection. Use the grade oil Ford recommends for the car.

Note that, if your engine is already using oil excessively and you have to add oil several times between changes, it's pretty much a matter of economics at that point. The engine already needs overhaul: the additional wear caused by cold-starting with single weight oil won't change that. However, if your engine doesn't burn oil, using a cheaper oil is a false economy.

I strongly recommend the use of a good synthetic oil!