Mexico’s oil is running out and unless it acts soon to boost exploration it could be importing fuel within a decade. That stark reality was spelled out this week by Felipe Calderón, the country’s president, announcing plans to give Pemex, the state-owned oil company, greater freedom and flexibility to ally with foreign partners. Mexico’s politicians should back him.

Mexico’s problem is two-fold. First, most of its oil reserves are offshore in the Gulf of Mexico, accessible only through advanced deep-sea drilling. Second, clauses in the constitution block the country from buying in this expertise.

High prices make resource nationalism wholly comprehensible. But Mexico’s approach – dating from its myth-creating nationalisation of oil in 1938 – is self-defeating.

Restrictions on overseas or private involvement in the Mexican industry prevent Pemex – which is badly run, inefficient and undercapitalised as a result of looting by the state treasury – from forming joint-ventures. That limitation, absurdly, even applies to state-controlled companies, such as Brazil’s Petrobras, a world leader in precisely the kind of technologies that Mexico needs.

These rules, more rigid than those in nearby communist Cuba, have ground exploration nearly to a halt. Proven reserves have declined from 20bn to 14.7bn barrels of oil since 2002. Mexico is replacing its current production at less than 20 per cent a year compared with more than 50 per cent – and often much higher – in the case of the world’s leading oil companies.

Falling production means the government will face further pressure on spending because it relies on oil to supply about 40 per cent of its income. The value of output lost since 2005 is equal to almost three times the budget for Oportunidades, the government’s much-applauded scheme to help the poor.

Mr Calderón is a better tactician than his predecessor, Vicente Fox, last year persuading Congress to back his plans for pension and tax reform. His proposals are modest. Pemex will stay firmly in public hands. Mexico’s constitution – a sacred cow for the nationalist left – will not be altered. The idea is to try to go round it, even though this may raise legal concerns for oil companies eyeing investments.

Time is short, partly because the government has been slow to unveil its proposals. But legislators should support him. Blocking change now and supporting calls to maintain the status quo would be self-destructive. Mexico’s politicians must seize this chance to reverse what will otherwise become a needless and tragic decline.