The United States is a highly developed mixed-market economy. It is the world's largest economy by nominal GDP, and the second-largest by purchasing power parity (PPP) behind China. It has the world's seventh-highest per capita GDP (nominal) and the eighth-highest per capita GDP (PPP) as of 2022. The U.S. accounted for 15.5% of the global economy in 2022 in PPP terms, and around 24.7% in nominal terms in 2022. Its firms are at or near the forefront in technological advances, especially in computers, pharmaceuticals, and medical, aerospace, and military equipment. The U.S. dollar is the currency of record most used in international transactions and is the world's foremost reserve currency, backed by the nation’s massive economy, stable government and legal framework, large U.S. treasuries market, extensive natural resources, highly advanced military, its role as the reference standard for the petrodollar system, and its linked eurodollar. Several countries use it as their official currency and in others it is the de facto currency. The nation's economy is fueled by abundant natural resources, a well-developed transportation infrastructure, and high productivity. It has the second-highest total-estimated value of natural resources, valued at US$ 44.98trillion in 2019, although sources differ on their estimates. Americans have the highest average household and employee income among OECD member states. In 2013, they had the sixth-highest median household income, down from fourth-highest in 2010. The largest U.S. trading partners are China, the European Union, Canada, Mexico, India, Japan, South Korea, the United Kingdom, and Taiwan. The U.S. is the world's largest importer and second-largest exporter. It has free trade agreements with several countries, including the USMCA, Australia, South Korea, Switzerland, Israel, and several others that are in effect or under negotiation. By 1890, the United States had overtaken the British Empire as the world's most productive economy. It is the world's largest producer of petroleum and natural gas. In 2016, it was the world's largest trading country as well as its third-largest manufacturer, representing a fifth of the global manufacturing output. The U.S. not only has the largest internal market for goods, but also dominates the services trade. U.S. total trade amounted to $4.2trillion in 2018. Of the world's 500 largest companies, 121 are headquartered in the U.S. The U.S. has the world's highest number of billionaires, with a total wealth of $3.0trillion. US commercial banks had $20trillion in assets as of August 2020. U.S. global assets under