To determine the amount of water in an oval pool, calculate the area of the oval (elipse) and multiply that by the depth, then take that volume and plug it into a conversion factor. There is a "rule of thumb" for finding the area of an oval. It makes for a good approximation and allows us to avoid the calculus. It's l(length) x w (width) x 0.8 which in this case is 30 x 17 x 0.8 = 408 ft2 for the area. Multiply that by the depth, 5.5 ft, and you've got 2244 ft3 for a volume. Water has about 7.48 gallons per cubic foot, so your pool will hold about 16,785 gallons of water when filled to the brim. Sloping sides will strip something off that figure, obviously.
About 26,406 gallons.
18,821 gallons.
24,000
It depends how deep it is.
300 gallons.
5,677 gallons
10,408 gallons.
About 2,550 gallons.
6,200 gallons.
181,248 gallons.
About 4,650 gallons.
3,398.4 gallons.
5,974 gallons.
1,770 gallons.
3384 gallons for every foot deep it is.