Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Oily Rain
Name: Benjie
Status: other
Grade: 12+
Location: SC
Country: USA
Date: N/A 

I read here that oil does evaporate:

with the churning of waves, rain, and time of year, do the answers suggest that one can expect oily rain in the Gulf Coast?

Crude oil is a mixture of any number of different organic molecules, some relatively light (such as methane) and some very heavy such as octane or kerosene. What will evaporate are the lighter molecules. The heavier molecules are what give oil its slick or oily feel. The chances of these evaporating quickly enough to affect the local weather is very small. So, no, you will probably not feel oily anything unless you are very close to the venting well.

If conditions were just right, you might get rain laced with say octane, but not rain that would feel oily to the touch. In addition, because the evaporation is occurring in the open ocean, winds should disperse the evaporated molecules widely. The chance of having a high enough concentration in any area such that the hydrocarbons could be detected by our five senses as very small indeed.

R. W. "Bob" Avakian
B.S. Earth Sciences; M.S. Geophysics
Oklahoma State Univ. Inst. of Technology

The first part of the question should be about the evaporation rate of crude oil.

I found the following paper from the Canadian Environmental Technology Department which addresses this issue:

It says that in a few days, light crude oil can evaporate as much as 75% of the starting oil mass And medium crudes up to 40%. Heavy or residual oils may only evaporate 10% of the starting oil mass.

I have never experienced an oily rain and I could not find any references to oily rain on the Internet except from a bicycler whose pant leg got soiled by oil from his chain.

My guess is that the overall volume of the atmosphere overwhelms any evaporated oil products And that an oily rain fall is highly unlikely. There may be some petroleum products in a rain fall, but they would not be detectable by people's normal senses.

Sincere regards,
Mike Stewart

Click here to return to the Weather Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory