Oklahoma City is 6.5 times larger than Amarillo, Texas.
Area: 257 km2 calculated
Amarillo is the fourteenth most populous city in the state of Texas, also the largest City in the Texas Panhandle, and the seat of Potter County. A portion of the city extends into Randall County. The population was 190,695 at the 2010 census. Wikipedia
Area: 1,682 km2 calculated
Oklahoma City is the capital and largest city of the U.S. state of Oklahoma. The county seat of Oklahoma County, the city ranks 27th among United States cities in population. The population grew following the 2010 Census, with the population estimated to have increased to 610,613 as of July 2013. Wikipedia