Benitez told the Liverpool website: "It's clear when you look at some of the other groups that ours could have been easier.
"Porto have good experience in the Champions League and have enjoyed a good record over recent seasons. They will be tough opposition for us.
"Marseille are a good side in the French league and they will know a lot about us which could make it more difficult.
"And you always know when you go to Turkey that it will be hard because of the travelling involved and the wonderful support they give their teams over there.
"I am always confident we can qualify but as ever the key will be winning the home games and picking up results away."