Ever since the 2007 announcement of the big deepwater Tupi oil field reserves in waters thousands of feet deep off Brazil, the nation has been moving up in the world of energy importance. As last week came to an end, the country celebrated extraction of the first oil from the pre-salt Santos Basin, where Tupi is located.

The event was marked by a pair of ceremonies; the first was on a production platform and attended by the president of Petrobras (NYSE:PBR), the nation's state oil company, while the second event, which included Brazilian President Luiz Inacio Lula da Silva, was conducted onshore.

Last week's festivities formally initiated tests of long-term production potential in the Tupi. Thus far, much of Brazil's crude production has come from the Campos Basin. There the water depths are relatively shallow. Tupi, however, lies below the far deeper waters of the Santos Basin. From 23,000 ft. below the surface, the trapped oil is capped by several thousand additional feet of technologically challenging salt, pressure, and extreme temperatures.

There remain unanswered questions about what geologists call the "lateral continuity" to the salt formations. The greater the continuity, the higher the likelihood that the field will produce for reasonable lengths of time without declines in pressure. To study these questions, Petrobras recently signed a contract with oilfield services leader Schlumberger (NYSE:SLB).

The Tupi field is expected to contain as much as 8 billion barrels of oil, although some estimates run much higher. Beyond that, Petrobras believes that the field likely is just a part of what could be a vast new oil province in the country's deepwater. Indeed, just this year ExxonMobil (NYSE:XOM) and Hess (NYSE:HES) announced a new discovery in a Brazilian pre-salt field.

At the same time, while lower commodity prices are causing oil and gas project expenditures to drop like proverbial rocks around the globe, Petrobras still plans to spend billions studying and developing the new fields during the next four years. In that context, it continues to keep deepwater drilling twins Transocean (NYSE:RIG) and Diamond Offshore (NYSE:DO) busy.

My Foolish investment thesis regarding Petrobras is really quite simple: If you have even the slightest interest in energy -- and you should -- you must be watching this company. While there are still questions about its new discoveries, your portfolio will thank you for monitoring the answers now that the tests have begun.

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Fool contributor David Lee Smith doesn't own shares in any of the companies mentioned above. He does welcome your questions, comments, or kibitzing. The Fool has a deeply drilled disclosure policy.