Edit: ditto for merchant navy...vast majority, nada. Even on a convoy with disastrous loss rate - unless carrying munitions. For instance, carrying wooden rifle butts qualified crew for medals but hold full of aviation fuel stored in foil lined hardboard cases didn't!
I am not sure if you are referring to gallantry medals or campaign medals, but in the case of the latter, the Merchant Navy was entitled to the same campaign medals and stars as the Royal Navy, with similar periods and areas of qualification. The type of cargo being carried was not a factor.
I have only ever physically seen a few groups of WW2 medals which contained the then maximum of five campaign stars, and they were all to Merchant Navy recipients, who tended to "get around" more than their RN equivalents. I suspect that with the introduction of the Arctic Star in recent years there will a few six star Merchant Navy groups around.