Albert Barnes Commentary Exodus 22:1

"If a man shall steal an ox, or a sheep, and kill it, or sell it; he shall pay five oxen for an ox, and four sheep for a sheep." — Exodus 22:1 (ASV)

The theft of an ox appears to have been regarded as a greater crime than the theft of a sheep, because it showed a stronger purpose in wickedness to take the larger and more powerful animal. It may have been on similar moral ground that the thief, when he had proved his persistence in crime by adding to his theft the slaughter or sale of the animal, had to restore four times its value for a sheep (compare the marginal references) and five times its value for an ox. However, if the animal was still alive in his possession , he only had to make double restitution.