Hi...
I don't think it's quite as simple as Rvrrat has indicated.
For you to view...
§ 135.243 Pilot in command qualifications.
(a) No certificate holder may use a person, nor may any person serve, as pilot in command in passenger-carrying operations --
(1) Of a turbojet airplane, of an airplane having a passenger-seat configuration, excluding each crewmember seat, of 10 seats or more, or of a multiengine airplane in a commuter operation as defined in part 119 of this chapter, unless that person holds an airline transport pilot certificate with appropriate category and class ratings and, if required, an appropriate type rating for that airplane.
So as you will see below, if you are engaged in Commuter Operations using a Multi-Engine Airplane, (other than turbojet powered), the aircraft may be single pilot certificated but you will need an ATP....which means 1500TT.
§ 119.3 Definitions
Commuter operation means any scheduled operation conducted by any person operating one of the following types of aircraft with a frequency of operations of at least five round trips per week on at least one route between two or more points according to the published flight schedules:
(1) Airplanes, other than turbojet powered airplanes, having a maximum passenger-seat configuration of 9 seats or less, excluding each crewmember seat, and a maximum payload capacity of 7,500 pounds or less...
The criteria mentioned in the previous post is certainly valid for some operations, but you should be aware of the differences.
Just more for you to think about.
Regards