aLEX Salmond has claimed that increasing tax on North Sea oil and gas will cost 15,000 jobs.  The First Minister has also warned Chancellor George Osborne that while he may not be about to kill the goose that lays the golden eggs,  he s in danger of disabling it .  Mr Salmond spelled out his concerns at a briefing on a paper the Scottish Government is sending to Mr Osborne setting out alternatives to ?2 billion supplementary charges the Chancellor announced in the Budget through a tax rise from 20% to 32%.  Mr Salmond said:  If nothing was done about the supplementary charge, the likelihood is there will be 15,000 less jobs than would have been the case without the supplementary charge.  What that means in revenue terms is, over the next 10 years, there will be one billion barrels of oil and gas equivalent less.  The options paper, UK Continental Shelf Tax Regime   Options For Reform, sets out three proposals Mr Salmond claims would be  more progressive , and reduce the tax on less profitable projects that would otherwise be shelved. His preferred option is the  investment rate of return allowance , which guarantees oil and gas companies a minimum rate of return on their investment.  The other two options are the  investment uplift allowance , which would also guarantee companies a minimum rate of return on investments before the supplementary charge was applied, and  extended field allowances    which would reduce the amount of tax oil and gas firms pay on their profits.  Mr Salmond, a former oil economist with the Royal Bank of Scotland, said: Putting forward these proposals is done with the intent of recognising that it is a legitimate objective of government to maintain the maximum income from oil and gas but to say that to make it optimal you have to look at sustaining investment over the longer term.  The industry s activity Survey