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 BG Group (LSE: BG.L) (NASDAQOTH: BRGYY) to see if its reported earnings have been distorted significantly by exceptional, one-off, or unusual items. I've extracted the following statistic:

Year to Dec. 31

2007

2008

2009

2010

2011

Profit before unusual items (£m)

3,021

5,495

3,824

3,885

5,179

Restructuring charges (£m)

-

(3)

-

-

(19)

Gain/(loss) on sales of assets(£m)

19

(24)

(134)

(215)

(310)

Source: S&P Capital IQ

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 BG Group reported cumulative profits before exceptional items and tax of £21.4 billion. However, aggregate exceptional costs came to £0.7 billion -- equivalent to 3% of cumulative "underlying" profits.

BG Group's profit and loss account looks very clean compared to pretty much every other company we've looked at in this series. That said, the increasing losses on the sales of assets is something shareholders will want to keep an eye.

Most of these costs have come from operational reviews, where BG Group has decided to trim back in a few, less successful areas. This isn't that surprising for an exploration business, as such outfits frequently attempt to fine-tune their asset portfolios. For example, the costs incurred in 2011 mostly came about following a review of BG's operations in Africa, the Middle East, and Asia.

With BG Group having recently warned of flat production next year, and a new chief executive taking charge soon once Sir Frank Chapman officially retires, we might expect to see a few more one-off items in the near future. So investors should keep a close eye on the accounts for both 2012 and 2013.

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.