I cant think of any difference, but the "Compact" version is cheaper than the CP99?

The compact has blowback and shoots bb's only. Where as the CP99 fires pellets in revolving mag's.

Looked at a pic of the Sport and the only differences I can see is the Safety indicator is white, my cp99 is red. And there is the writing on the top slide is different. Not actually had time to look at the spec's but may be different.

Tony