What's the difference in information from the API report and the EIA report?

Hi Guys,

Another noob question from me, just want something cleared up if anyone can help?

EIA Report : shows the amount of commercial crude held by US firms.

API Report : Shows inventory levels of crude (per investing.com).

My question is, what is the difference between the two figures? they're obviously reporting different statistics but I can't get my head around what they might be?

thanks

Guys I asked on another website. The trader (who is a pro) said that the API is a guess of the EIA figure using various sources.

check out this

http://www.marketwatch.com/story/whose-petroleum-supply-data-should-you-trust