You are generally eligible to ship one vehicle overseas with PCS orders to an OCONUS location. The shipping of one vehicle is done so at the expense of the government. If you wish to ship a second vehicle, it will generally have to be at your expense through a commercial shipping company. Before shipping a second vehicle, you should always check with the transportation office first for any restrictions.
There are size limitations with shipping. The government covers the expense up to 20 measurement tons with one measurement ton equaling 40 cubic feet. Most cars will easily fall into this range. You could exceed this if you are shipping a full size pick up truck or RV. Any overage above 20 measurement tons will be expensed to the military member.
There are time limitations for shipping your POV overseas. If the tour is longer than one year, you have 90 days to have the vehicle arrive at the port from the time the military member or dependent leaves for overseas. If the tour is less than one year, you have 30 days to get your vehicle to the port. If you miss this window, the vehicle may still be eligible to be shipped but you will need approval from the commander overseas.
If your vehicle is a lease or has a lien against it, you must obtain permission from the lease holder or lien holder before moving the vehicle overseas.
This pdf file contains a great deal of information about shipping your POV including port locations.
Track your POV during a move.