(Keldon Oasis isn't a spell.)
Keldon Oasis enters the battlefield tapped unless you pay .
, : Tap target artifact with converted mana cost X or less.
: Add or to your mana pool.
Put Keldon Oasis on top of your library: Add to your mana pool.
.
, 
: Tap target artifact with converted mana cost X or less.: Add 
or 
to your mana pool.
to your mana pool. 
