I'm only answering to sum up to combine the 2 answers, and add drill percentages

Read Mathias711's answer for available storage loot, available collector loot is 50%, for dark elixir drills, it's 75%. This is confirmed here

"The percentage of Gold and Elixir that can be stolen from mines and collectors is 50% and is capped only by the storage capacity of the resource collector."

"The percentage of Dark Elixir that can be stolen from drills is 75% and is capped only by the storage capacity of the drill."

I'm only answering to combine the 2 answers, and add drill percentages

Read Mathias711's answer for available storage loot, available collector loot is 50% (for elixir collectors and gold mines), and 75% for dark elixir drills. This is confirmed here

"The percentage of Gold and Elixir that can be stolen from mines and collectors is 50% and is capped only by the storage capacity of the resource collector."

"The percentage of Dark Elixir that can be stolen from drills is 75% and is capped only by the storage capacity of the drill."

I'm only answering to sum up to combine the 2 answers already here

Read Mathias711's answer for available storage loot, available collector loot is always 50%.

"The percentage of Gold and Elixir that can be stolen from mines and collectors is 50% and is capped only by the storage capacity of the resource collector."

I'm only answering to sum up to combine the 2 answers, and add drill percentages

Read Mathias711's answer for available storage loot, available collector loot is 50%, for dark elixir drills, it's 75%. This is confirmed here

"The percentage of Gold and Elixir that can be stolen from mines and collectors is 50% and is capped only by the storage capacity of the resource collector."

"The percentage of Dark Elixir that can be stolen from drills is 75% and is capped only by the storage capacity of the drill."