Big oil has lost big money for investors.

In the past year, as crude prices have fallen more than 55 percent, the nine biggest Western oil companies have shed a combined $400 billion in market cap, according to data pulled by FactSet. But despite the staggering decline, one expert sees rare opportunity in the space.

“It’s important to remember that going back over the last 20 years in the equity market, whenever you have a secular change such as technology in 2000, financials in 2007 and 2008 and now energy, it takes about two years for a real capitulation washout,” Larry McDonald said Wednesday on CNBC’s “Power Lunch.” Energy stocks have been steadily declining since June 2014.

Read the remainder of this article on CNBC’s website.  

More from CNBC:  

http://www.cnbc.com/2015/08/12/us-stocks-open-sharply-lower-as-yuan-extends-slide.html 

http://www.cnbc.com/2015/08/12/driving-costs-the-same-as-it-did-in-the-50s.html

http://www.cnbc.com/2015/08/13/will-greece-be-saved-by-solar.html