Amazon (NASDAQ:AMZN) reports earnings this Thursday, after market close. Shares are up 36% year to date, handily outperforming the S&P 500's 22% gain. With shares basically trading at an all-time high, investors will be watching the report closely. What, in particular, should you watch for?

Is heavy investment in Amazon Instant Video content paying off?
Amazon has been on a spending spree for video content. Right along with Netflix (NASDAQ:NFLX), Amazon has upped the ante in its search for content. Having expanded its deal with Viacom, and having launched a handful of original series, the costs of Amazon's efforts to provide a competitive streaming video service are mounting. In fact, the new comedy series Betas is alone estimated to cost Amazon between $10 million and $50 million. Is this wild spending worth it?

Amazon certainly isn't alone in massive spending on original content. Netflix and Hulu are also getting aggressive. On a positive note, Netflix must see some benefit, because when it announced earnings yesterday, the company said it plans to double its investment in original content in 2014.

What about groceries?
Grocery delivery service AmazonFresh is frequently heralded as one of Amazon's major growth opportunities. Not only could the service help Amazon tap into a massive $220 billion U.S. consumer packaged goods market, but it could be a profitable operation, too. AmazonFresh's operating margins could be as high as 13%, according to Bernstein analysts. 

AmazonFresh is now operating in Los Angeles and Seattle. It will expand to as many as 20 other urban areas (including some outside the United States) in 2014 if current markets go well, according to Reuters. Is Amazon ready to expand the service further?

Beat revenue estimates
Last, and probably most important, Amazon will likely need to beat revenue estimates to keep the Street excited about its stock at $325 per share.

With spending varying dramatically, especially given investments in fairly new projects including original content and AmazonFresh, earnings-per-share results usually don't matter as much as revenue when the company reports earnings. In fact, analysts are estimating Amazon will post an EPS loss of $0.09 per share.

Revenue, however, should take center stage, as usual. On average, analysts expect revenue of $16.76 billion, up 21.4% from the year-ago quarter. Last quarter Amazon posted year-over-year sales growth of 22%, so revenue growth below 21% would probably be a disappointment.

For long-term investors, revenue growth is particularly important. If Amazon is going to continue to forgo earnings, then it'd better be gaining massive market share so that when profits are finally reported it can generate a meaningful cash stream.

Keep an eye on video content, AmazonFresh, and revenue growth. Other than that, investors might also want to watch for an update on the company's Kindle business. Is the strategy to sell hardware at cost and subsequently profit on content sales still working?

Fool contributor Daniel Sparks has no position in any stocks mentioned. The Motley Fool recommends and Netflix. The Motley Fool owns shares of and Netflix. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.