1. The petrodollar refers to Organization of Petroleum Exporting Countries (OPEC) namely Saudi Arabia that accept dollars for oil. Oil bought in dollars creates demand for dollars

2. Saudi invests dollars back into US currency. Saudi has $584 billion in foreign reserves with most of it invested in dollar denominated securities. Since 2014, Saudi has spent $139 billion of its reserve. (http://money.cnn.com/2016/04/19/investing/saudi-arabia-threat-dump-us-assets-911-bill/)

3. During a commodity boom, oil-rich nations accumulate billion in dollar reserves investing in US debt and other securities.

4. As oil and other commodity prices decline less demand for investing petrodollar in European and US debt, occurs. OPEC is removing liquidity out of the market as a result. Reserves have declined in Angola, Algeria, Nigeria, Oman, and chile. In 2015, OPEC was expected to sell $380 billion in oil sales, a $350 billion drop from 2014. In 2015, oil rich countries will sell $200 billion in assets to generate cash. Bond purchases are necessary to keep interest rates low. (http://www.bloomberg.com/news/articles/2015-04-13/oil-rich-nations-burn-through-petrodollar-assets-at-record-pace)