Many mobs in EQOA have a chance of dropping rare items - those with magical qualities such as procs or statistic improvements.
There are four categories of drop rates, in terms of rarity.
It is unknown if the same scale of rarity applies to named mobs with specific drops (that is, if a named mob may have a common, uncommon, rare, and ultra-rare drop), or simply to generic mobs who draw from global, regional, or mob-specific loot tables.
It is likely that common rarity items have an approximate 4% drop rate per mob (that is, 1 in 25).
It is likely that uncommon rarity items have an approximate 1% drop rate per mob (that is, 1 in 100).
It is likely that rare rarity items have an appropriate .1% drop rate (that is, 1 in 1000).
That likelihood of ultra-rare drops is largely unknown, as reliable testing becomes difficult at this degree. It is plausible that ultra rare items have a drop rate in the range of .01% (that is, 1 in 10000).