Sparked by surging oil, a dramatic rise in the value of old plastic is encouraging waste companies across the world to dig for buried riches in rotting rubbish dumps.

Long a symbol of humanity's throw-away culture, existing landfill sites are now being viewed as mines of potential which as the world population grows could also help bolster the planet's dwindling natural resources.

"By 2020 we might have nine billion people on the planet, we could have a very big middle class driving millions more cars, and we could be in a really resource-hungry world with the oil price climbing and a supply situation in Libya, Russia and Saudi where natural gas is limited," said Peter Jones, one of Britain's leading experts on waste management.

"It is those drivers, those conditions, which will encourage the possibility of landfill mining."

In Britain alone, experts say landfill sites could offer up an estimated 200 million tonnes of old plastic - worth up to £60 billion at current prices - to be recovered and recycled, or converted to liquid fuel.

As many oil analysts predict oil prices will stay above $100 a barrel, waste experts in America, Europe and across Asia have been conducting pilot projects to recoup old plastic and other waste materials.

Prices for high quality plastics such as high-density polyethelenes (HDP) have more than doubled to between £200 and £300 per tonne, from just above £100 pounds a year ago, according to experts in the waste industry.

With this in mind, leaders of the world's waste management industry are planning to come together in London in October for what is being billed as the first "global landfill mining" conference.

"Once plastic is in a landfill site, it pretty much sits there doing nothing - and the beauty of that is that you're able to go back and recapture it in the future," said Peter Mills, a director of waste and recycling company New Earth Solutions, who is scheduled to speak at the conference.

"There are some really buoyant prices around because plastic is all manufactured from oil, so as the raw price of oil goes up, every commodity derived from it goes up accordingly."

According to the Organisation for Economic Cooperation and Development (OECD), the amount of household rubbish thrown out across the world is expected to rise to about three billion tonnes a year by 2030 from 1.6 billion tonnes in 2005 - or about one kilogramme per person per day in 2005.

Many of the world's rich countries send about half of that trash to landfill, but the OECD projects that rate will fall to 40 per cent by 2030 as governments promote recycling - of materials such as metals, glass and paper - or incineration to generate heat or electricity.

"Over a period of a very long time - many decades - we have had a policy of burying whatever we can in landfill sites - so there are valuable resources in those sites," said Steve Whatmore, of Orchid Environmental, a waste and recycling firm.

"And wherever there are valuable resources, there is always the temptation to investigate whether it is worth recovering them. The logic is sound, but the practicalities are complex - and you have to balance those out with the commercial viability." Landfill mining - digging in dumps for valuable materials - is hardly a new concept, and already viable for some.

Images of poor, often homeless people scavenging waste to sell from landfill sites in Asia and South America have already provided evidence there is money to be made from other people's rubbish.

William Hogland, a professor in Environmental Engineering and Recovery from the University of Kalmar in Sweden, also points to previous instances of dumpsite mining in Israel in the early 1950s where the soil - enriched with rotting waste - was recovered and recycled to improve soil quality in orchards.

And certain US states have since the 1980s mined waste from landfills to be used as fuel for incineration to produce energy.

"Several pilot studies have been carried out for research or pre-feasibility studies in countries in Europe, but also in China, Japan and India," he said. For global waste experts, not everyone's rubbish is the same: different sites have different potential and an individual country's or region's dumps show characteristics relating to the culture, historical development and economic climate.