What are the differences between commerical pilots license, and airline transport pilots license?

I am majoring in aviation at Liberty University, and I already have my PPL, and I was wondering. Since I am going for my commercial license, does that mean that I can become a pilot for like Delta, and fly passengers, or do I need my airline transport pilots license to fly passengers?

Your question has been answered, but I have my can of bs spray out for your claim of what/who you are.

While a commercial license will allow the pilot to be paid for his services just like an ATP, the commercial license is limited to the type of aircraft that can be flown. The ATP is also all inclusive in that the instrument rating is included in the license. The ATP requires a minimum of fifteen hundred hours to obtain and is broken down to such things as instrument, night and cross country hours.

The big difference is that the ATP is allowed to fly as captain on large jet aircraft for hire. A commercial pilot could only fly as copilot. And BTW, there is no such thing as a part 15 airliner. There are two types of commercial air carrier certificates issued to a company. Scheduled airlines are issued a part 121 cert. Charter falls under part 135.

For flying people around in a twin a commercial license is OK but if you are going to be flying a Part 15 airliner, then you need an ATP and the hours that go with it.