How to create Drake Egg Oil
Drake Egg Oil is an item that was introduced during the Velious expansion and made with Brewing. All you need in order to make it is a Drake Egg and a Water Flask, the Drake Egg is the hardest of the two reagents to find. Depending on what expansion your server is on determines where you'll want to go to farm it.
Those of you reading this on P99 or on Corinav you'll want to head to Skyshrine and farm the drakes in this zone or just Forage to find Drake Eggs. Additionally, you can Forage in Temple of Veeshan and get not only Drake Eggs but Wurm and Dragon Eggs too!
Combine both of these items in a Brewing Barrel.
If you're playing on a server that's up to TSS (The Serpent's Spine) your options for farming Drake Eggs become much more plentiful.
Sunderrock Springs - Drake Egg Farming Location
This is arguably the best location in the game for you to farm Drake Eggs from enemies. The Drakes here are 60 - 70 and can be pretty darn tough if you're around their level - it would be faster for you to just Forage the eggs. Those of you reading this that are much higher level than these drakes - you'll benefit most from farming here.
Crescent Reach - Drake Egg Farming
Crescent Reach is the lowest level location you can farm Drake Eggs in the entire game. The drakes here are 3 - 11.