Apple’s stock reached an all-time high of $301.96 on Wednesday. In late September it became the world’s second biggest company by market value. With a current market capitalization of $274 billion, Apple is second only to oil company Exxon Mobil’s market capitalization of $331 billion.

The company releases earnings next week. In anticipation of strong results, investors have sent Apple’s shares up over 6% in the last five trading days.

Apple’s stock is up nearly 43% in 2010 and is up over 58% in the last 12 months. It hit an all-time high of $301.96 per share on Wednesday before closing at $300.14. Exxon Mobil’s stock is down 4.5% year to date and is down 7.3% in the last 12 months.

Could Apple become the most valuable company on the U.S. stock exchange? If Exxon Mobile continues to slide at its current annual pace, Apple would need to increase in value by 12% in 12 months to overtake the oil giant. Given the company’s ability to create innovative, in-demand products and successfully ride them through a long life cycle, it’s very possible Apple can continue to grow for a number of years.

As points of comparison, Microsoft’s market capitalization is $219 billion, Walmart’s is $196 billion, IBM’s is $177 billion, Google’s is $173 billion and Amazon.com’s is $69 billion. In the music world, Live Nation’s market capitalization is $1.65 billion and Warner Music Group’s is $784 million.

Market capitalization is the value of a company’s stock and equals its stock price multiplied by the number of shares outstanding. It can be thought of as a claim on a company’s future cash flows. Apple has less net income than Exxon Mobil ($3.2 billion versus $7.5 billion last quarter) but more growth opportunity. Market capitalization is different than the book value of a company, which takes into account a company’s assets. Apple has about $36 billion in assets while Exxon Mobil has $62 billion. Nor is market capitalization a company’s price tag if it were to be acquired.