LONDON -- Right now I'm trawling through the FTSE 100 (UKX) and double-checking for blue chips that may be flattering their profits.

You see, many companies these days report "underlying" earnings, which are calculated by excluding costs the firm deems to be "exceptional." Trouble is, some companies are more cavalier than others when it comes to sweeping awkward expenses away from the headline figures.

Today I'm looking at Royal Dutch Shell (LSE: RDSB.L) (NYSE: RDS-B) to see if its reported earnings have been distorted significantly by exceptional, one-off or unusual items. I've extracted the following statistics courtesy of S&P Capital IQ:

Year to Dec. 31

2007

2008

2009

2010

2011

Profit before unusual items (£m)

23,362

32,341

13,432

21,357

33,646

Gains on sales of assets and investments (£m)

2,164

2,794

484

2,098

-------

Asset writedowns (£m)

(79)

(255)

(903)

(746)

(749)

While annual figures can provide some insight into how a business has performed, I reckon looking back over several years provides a better view of possible problems in relation to one-off costs.

So between 2007 and 2011, my stats tell me Shell reported cumulative profits before exceptional items and tax of £124.1 billion. However, aggregate exceptional costs came to £4.8 billion -- equivalent to just 4% of cumulative "underlying" profits.

Shell's profit and loss accounts look cleaner than the other big companies I've looked at recently in the series.

Asset writedowns have been very small in relation to its overall profits, and less than half the amount written down by BP (LSE: BP.L) (NYSE: BP) over the same five-year period.

But Shell has also consistently made profits each year by selling assets and investments, suggesting it's also been fairly prudent when it comes to valuing items in its accounts.

Somebody who always studies earnings numbers in detail is Neil Woodford, the U.K.'s leading equity income fund manager. Woodford's portfolios thrashed the FTSE 100 during the 15 years to 2011 and this exclusive Motley Fool report -- which can be downloaded free today -- reviews his favorite blue-chip shares for 2013 and beyond.

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