LONDON -- Not many companies can currently provide you with a 5.5% dividend income from a payout that hasn't been cut for more than thirty years.

One company that can, however, is Royal Dutch Shell (LSE:RDSB) (NYSE:RDS-B), the world's third-largest oil company. In 2012, Shell delivered net profits of $26.5 billion on sales of $467 billion -- that's more than the GDP of Finland and Austria.

Although there is no guarantee that the firm will maintain its impressive dividend record, Shell's payout is probably one of the safest in the FTSE 100, with more than three decades of consistency behind it.

A tax-efficient income
There's no denying that dividend income is the main reason for owning shares in Shell. The firm has provided an average dividend yield of 5.2% over the last five years, 60% higher than the current FTSE 100 average of 3.2%.

Shell pays a quarterly dividend and recently announced a 2% increase to its fourth-quarter payout for 2012, as well a planned 4.7% dividend increase for the first quarter of 2013. In total, analysts expect Shell's payout to rise by 7.9% in 2013 -- more than twice the rate of inflation.

By holding Shell shares within an ISA (just click here for more information about the benefits of ISAs), you can ensure that this generous income does not attract any further tax. This could really boost your returns over the long term, especially if you are a higher-rate tax payer.

Profit from scale
Shell is one of the world's five super-major oil companies, meaning that it is one of very few that have the combined financial and technical might needed to take on the very largest of projects.

One of the areas the company has focused on is increasing its share of the global gas market, and around half of Shell's production is now natural gas. This production provides the group with a more diversified production profile and should help it adapt to future changes in demand.

At the end of 2012, Shell was producing 3.4 million barrels of oil equivalent per day, and had proved reserves of around 13.6 billion barrels. Shell reckons these reserves would maintain production for another eleven years, but it's focused on growth, and is currently developing a further 20 billion barrels of resources across 60 projects.

2013's top ISA income stock?
If you like the idea of using an ISA to hold high-yielding income shares, then as well as Shell I'd also recommend you take a look at the Motley Fool's latest free report, "The Top ISA Income Stock for 2013".

You see, the company analyzed in this report currently offers a yield of 5.7%, and the Fool's expert analysts believe that its current share price of 700 pence could be 20% below its true value. To learn more, then click here to download your free copy of this special report, while it is still available.

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Roland Head owns shares in Royal Dutch Shell. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.