In science it is best to continue research, and rinse and repeat. This allows for a stronger hypothesis if you're results are the same every time, or change your hypothesis if you stumble upon new results. <span />
An oxygen atom is 16x more massive than a hydrogen atom.
You can figure this out by comparing the atomic masses of the two elements: oxygen has an atomic mass number of 16, and hydrogen has an atomic mass number of 1. Thus, an oxygen atom is 16 times more massive than a hydrogen atom.