Steve Jobs -- or is it Tim Cook? -- runs a tight ship at Apple

The company's revenues may have exploded, but its operating costs have not.

Source: Asymco, using calendar quarters. Click to enlarge.

As they grow larger, most enterprises tend to get a little soft around the belly.

Not Apple (AAPL). In the past five years, while its revenues were growing more than 250% -- from $5.75 billion in Q4 2005 to more than $20 billion last quarter -- its operating expenses actually fell as a percentage of sales.

The chart above, which tracks Apple's R&D and SGA (selling/general/administrative) expenses since 2005, shows them shrinking from nearly 17.5% five years ago to 10.2% today.

"Keep in mind," writes Asymco's Horace Dediu, who produced the graphic, "that in many ways Apple is doing the job for all the knockoffs, copycats and ripoff artists in the industry. It's a feat of efficiency that boggles the mind."

NOTE: Although Steve Jobs takes the bows, credit probably goes to Tim Cook. He is, after all, the man in charge of operations.

[Follow Philip Elmer-DeWitt on Twitter @philiped]