OXYGEN SENSORS

I believe so, yes. Two on each cylinder bank, before and after the catalytic converter. Someone else here can probably verify that for sure.

It's highly unlikely that all four went bad at the same time, but just to be sure can you tell us what the codes were that the mechanic pulled out of the vehicle? Vehicle computers are dumb, and sometimes a related problem can point to the oxygen sensors as being at fault when in reality they are only the messengers. It does no good to shoot the messengers.