The above chart shows the growing impact of Amazon Prime (discussed here, here, and here on MobyLives) on Amazon’s bottom line. In a commentary accompanying the chart, which was posted on PaidContent, Jeff Bailey of Y Charts notes that Amazon’s net shipping costs “were up 82 percent for the first three quarters of 2011, to $1.5 billion. If that rate of increase continued in the crucial fourth quarter, Amazon’s total 2011 net shipping costs would be about $2.5 billion.”

As for what Wall Street thinks, Bailey notes “The stock market seems mostly indifferent to Amazon’s margin compression, with the recent reduction in its valuation still leaving the stock’s PE at nearly 100. Investors instead seem focused on revenue growth, which is super largely thanks to Prime.”

In November the Wall Street Journal attempted to guess the cost of Amazon Prime. According to an analyst quoted in the Journal, “Amazon spends more than $90 a year for each Prime customer, losing $11 annually for each subscriber. Of the $90, $55 comes from shipping costs and $35 comes from acquiring digital video content.”