

For the last oil rig, I do not check for load, I just instruct the oil barge to go straight to port to unload and then start the round all over again. If it is less than 95% (adjust for size of oil barge) it goes to the next oil rig, but if it is 95% or more then it goes to port to unload or transfer.

What this does is goes to an oil rig, after it loads the petroleum, it checks to see how much it has loaded. Go to Oil Rig 4 (Last oil rig, or rig closest to port)
OPENTTD CONDITIONAL ORDERS FULL
Its also possible to to the reverse, after every " Go to place" order add a conditional order with "If less than 80% full Go to Order N+3" (where N is the order number of the " Go to place", N+1 is the conditional order, etc). The downside to this is that the last stations will be visited less often than the first ones. When the ship is done with loading somewhere it will check that order, and if nearly full it will go back to the first order (change the numbers if this is undesirable). The way I usually do this is, after every " Go to place" order add a " Conditional order jump" with something like "If 80% full Go to Order 1".
