Scroll compressors are provided with vapor injection or by-pass ports that will allow greater flow of refrigerant through the port than was the case in the prior art. The prior art has typically utilized a single injection port having a diameter equal to or slightly larger than the thickness of the scroll wrap. In this way, the scroll wrap is able to prevent or restrict cross-flow leakage from the port from passing between the two compression chambers. However, this single port has also limited the amount of refrigerant that can be returned. In one embodiment, the present invention utilizes a plurality of ports generally spaced along the length of the wrap such that cross-flow can still be prevented while providing a greater cross-sectional flow area into or out of the compression chambers. In another embodiment, the several ports may be replaced by a single elongated port. Further, if cross-flow leakage is not a particular problem, the ports may be positioned such that they begin to communicate, and stop communicating, serially, with the two chambers.