Have to agree with Rotates Lowly on this one! On aircraft like the B727-200 you pay a penalty of almost 10% for the fuel you are tankering FAJS-FACT(100kg burnt for every ton carried). The 737-200 is in the 3% range, still not worthwhile inside our borders.
You only tanker if there are no fuel on the other side (like in Zim), or if the fuel price is through the roof (like in Zim).
Fire away!