West Texas Intermediate (WTI) is the most important US benchmark crude oil. WTI crude oil is of high quality and can produce a high proportion of petrol. A light sweet (low sulpher) crude oil.
WTI is widely traded, as are derivatives based on it, for example through the CME and it is very often used as the benchmark for US oil prices.
Historical prices are available on the web through the US Energy Information Administration
Because ot its low API gravity (lightness) and sulpher content, WTI generally trades at higher prices than other major benchmarks such as Brent (itself a light crude), however, as it is a US measure, geographical differences in supply or demand can sometimes reverse this.