Someone should write an article titled:
The Rise and Fall of decline rates

It's actually a huge issue. After URR and decline rates, what else is there? (said with tongue in cheek)

We do have empirical data but even that varies widely. The IEA says 9%, but maybe 6.5% with good technology and field management, and wether the field is old or young, small or large, onshore or offshore

I remember Euan Mearns saying "the tea leaves say 5%"

Westtexas points to the lower 48 and North Sea and I think comes up with 4.8% as an aggregate.

I heard that Slumberger says 8% is their rule of thumb

and what is an undulating plateau but a decline rate in disguise?

Polytropos,

The 3.5% annual decline rate is an observed decline rate from the 2002 peak to now, noting that the 3.5% is only a rough estimate due to the production volatility caused mainly by hurricanes. The annual decline rate used going forward is 7.9% which is roughly equal to the current extraction rate, assuming remaining recoverable oil of 6.5 Gb. The change from 3.5% to 7.9% may occur in early 2011 as planned capacity additions decrease sharply in 2011.

Assuming US GoM of 23 Gb and using historical GoM production data from the EIA, the following extraction rate history is shown below.
http://tonto.eia.doe.gov/dnav/pet/pet_crd_crpdn_adc_mbblpd_m.htm

The most recent data month is Jan 2009 and shows a record annual extraction rate of 8.2%. This high extraction rate may be caused from high production ramp up at new large projects such as Thunder Horse. However, it might be partly caused by low oil prices forcing some operators to temporarily increase extraction rates to generate more revenue. It appears that a more reasonable annual extraction rate should be about 7% which implies that the Jan 2009 GoM production rate should be about 1.25 mbd rather than the EIA's actual 1.45 mbd.

The hurricane risk and the financial need to quickly recover the large investments for deepwater production force the oil companies to extract oil at very high initial rates. In March 2008, the IEA discussed non OPEC decline rates and found that US offshore average annual decline rates for mature fields were almost 20%. In addition, the IEA stated that "newer fields in these areas - often deepwater, smaller accumulations of oil - are also prone to rapid build to plateau, followed quickly by sharp decline."
http://omrpublic.iea.org/omrarchive/11mar08sup.pdf

For simplicity, I used a constant 7.9% annual decline rate for forecasting the production rate. In reality, the future annual decline rates will oscillate. In 2008 and 2009 there have been large capacity additions of about 0.5 mbd from Blind Faith, Neptune, Thunder Horse, Shenzi and Tahiti. This should keep the decline rate low. In 2010 there is another addition of 0.2 mbd from Perdido Hub, Chinook, Cascade and Phoenix. However, there are few planned additions from 2011 to 2014 which probably means that the annual decline rates will be greater than 8% starting in early 2011.
http://en.wikipedia.org/wiki/Oil_megaprojects

The IEA's 2009 Medium Term Oil Market Report, to be released by the end of this month, will probably give an update on offshore decline rates.
http://omrpublic.iea.org/mtomr_june09.htm