Federal officials acknowledge that the top kill carries a risk of breaking open the well or the BOP and exacerbating the spill. "We're carefully looking at all the pressures involved--what the BOP can handle, what the down-hole [pipe] can handle," says Lars Herbst, director of field operations in the Gulf for the U.S. Minerals Management Service (MMS), the federal regulator that both sells offshore oil and gas leases and regulates the resulting drilling.

Paul Bommer, a senior lecturer in petroleum engineering at the University of Texas at Austin, says he believes the junk shot will prove necessary. But he also sees it as a gamble--the junk shot could fail to block the BOP and further damage and open up the riser. "The bent riser is the weak link. The riser probably does not have the pressure rating of the BOPs and possibly could rupture," says Bommer.

Members of Congress called for tighter regulation of offshore drilling this week, and President Obama's interior secretary, Ken Salazar, announced plans to split the MMS's offshore oil promotion and permitting functions. Oil and gas drillers, meanwhile, are already adopting more and better technology in a bid to ensure that a current moratorium on issuing drilling permits does not turn into permanent restrictions.

Newman told senators that acoustic triggers should be added to BOPs to enable remote activation. BP documents released by Congressional investigators show that it has initiated subsea testing of the emergency mechanisms on BOPs, hitherto subject to testing only prior to installation on the seabed.

Shell, which is currently drilling seven wells in the Gulf, revealed extra precautions last week for an exploratory drilling program it intends to launch in the Arctic in July. These include doubling the deep-sea safety inspections of their BOP and prebuilding a "coffer dam" to cap blowouts.

Environmental activists are increasing pressure on the Obama administration to require tough environmental assessments before further drilling is authorized. For instance, the Tucson-based Center for Biological Diversity and a former environmental contractor for BP filed a notice of intent to sue the MMS, accusing it of violating federal law by issuing drilling permits for the Gulf without taking account of impacts to endangered species and marine mammals such as sperm whales, bottlenose dolphin, and the Florida manatee.

Center for Biological Diversity senior attorney Myoko Sakashita says the threats are even greater in the Arctic, dismissing as "meaningless" Shell's promised technology upgrades there: "In the Gulf, the waters are relatively calm and response is nearby. There are no measures that can be taken that would make drilling in the remote, frozen Arctic safe."