How many gallons of water does it take to fill a swimming pool that is 5'x30'x4'?

The formula for figuring out the amount of gallons is on the back of pool chemical containers. I am not sure what the formula is for an oval.

Check here: http://www.poolspa.com/calculator/

If the pool floor slopes uniformly from end to end, the average depth can be found by adding the deepest and shallowest depth measurements and dividing the results by two. If the pool's dimensions are in feet, the volume will be in cubic feet. One cubic foot of water equals 7.5 gallons.

Example: The water volume of a pool 60 ft. long, 30 ft. wide and that slopes in depth from 3 ft. to 10 ft. is as follows: 30 x 60 x ((10 + 3)/2) = 11,700 cubic ft. of water 11,700 x 7.5 = 87,750 gallons