1) For each player, we store a 'drop potential'. Your drop potential gradually increases, the more time you spend risking items on a PvP world. 2) When you get a successful kill, a portion of the drop potential you have accumulated is used up to generate your drop. How much of your accumulated drop potential is used depends on the kill. Any unused drop potential is saved up and carried over to any future kills. 3) Finally, the portion of drop potential used determines which drop table is used to generate your drop. Generally, the higher your drop potential, the higher the AVERAGE value of the drop table your drop will be chosen from. http://news.runescape.com/newsitem.ws?id=1535