"It's working as planned and we are very slowly increasing the rate that is coming from the riser tool up to the surface," Kent Wells, BP's senior executive vice-president, said.
"So we do have oil and gas coming to the ship now."
But Wells said it is too early to tell how much oil had been successfully siphoned off.
Preparations for an operation to inject mud into the well to stop the leak for good are ongoing and should be completed in seven to 10 days, he said.
Previous attempts to contain the spill have failed, including initial attempts to use robotic submarines to insert the 1.6km tube into the underwater oil pipe.
The tube could capture more than three-quarters of the leak, although the company must also contend with a smaller leak that is farther away.
Al Jazeera's Nick Spicer, reporting from Grande Isle, Louisiana, that the operation has done little to address fears of a possible environmental catastrophe.
"There's controversy about the rate at which oil has been leaking out of that shattered well head at the bottom of the Gulf of Mexico," he said.
"There's [also] controversy where I am about the dispersants that BP has been using with the authorisation of the federal government.
"Fishermen here fear that the use of that chemical, which is not good for human beings, could be very toxic for marine life and could endanger their lives for years to come."
BP began spraying chemical dispersants beneath the surface of the sea on Saturday, a contentious development because it the procedure had never been carried out underwater before.
Dispersants break down the oil slick into smaller particles, which are then more easily broken down by natural processes.
A relief well is being drilled to stop the leak permanently but it is still months away from being completed.