On Wednesday, ratings agency S&P Global cut its outlook on Exxon Mobil ( NYSE: XOM ) to negative, citing ( registration required ) weak credit measures, which means that the world's largest publicly traded oil producer could end up losing its double-A-plus rating in the next two years. The update comes 13 months after Exxon Mobil lost its coveted triple-A credit rating. However, I believe investors shouldn't fret over the latest downgrade.