When OPEC countries have increased oil price substantially, first in 1974, then around 1980, this had substantial positive effect on inflation in oil consuming countries, like the USA and Europe; see http://www.frbsf.org/education/files/drecon_0301a.jpg .
Now oil prices have dropped a lot. Will this cause deflation? Here is a discussion: http://www.economicshelp.org/blog/11738/oil/impact-of-falling-oil-prices/