BP says the 100,000 figure is not relevant as it is not based on reality.
US lawmakers have repeatedly accused BP of not being straightforward about the true size of the spill.
Mr Markey - a senior Democrat and chairman of one of the committees investigating the Gulf spill - said the document raised troubling questions about what BP knew about the size of the spill and when they knew it.
"First they said it was only 1,000 barrels, then they said it was 5,000 barrels, now we're up to 100,000 barrels," he told NBC's Meet the Press programme. Read the full report here.
Source: BBC News, UK