Complex sentence: In 2011, petroleum extraction accounted for 98% of the country's exports and contributed to 60.2% of Gross Domestic Product, but in the following year production declined drastically to about 14%.
Split into simpler sentences: In 2011, the petroleum extraction accounted for 98% of the country's exports and contributed to 60.2% of Gross Domestic Product (GDP). But in the following year production declined drastically to about 14%.