The Deepwater Horizon, which drilled the deepest oil well in history back in September of last year, sank on the 22nd of April after being rocked by a massive explosion that claimed the lives of 11 workers on the rig. Now, that well, 5,000 feet under the surface of the water, is continuing to pump somewhere to the tune of 200,000 to 400,000 gallons of oil into the Gulf of Mexico a day. Unfortunately it's gone on long enough that all that oil is clearly visible from space.
NASA has been tracking the spread of the slick with its Terra satellite, using the onboard Moderate Resolution Imaging Spectroradiometer (or MODIS) instrument to see it in natural color. That triangular shape you see on the right hand side of the picture above is where the sun is reflecting off the oil that's reached the surface and, as you can see by the legend in the bottom left, it's over 15 miles across.
NASA is using the data collected from the Terra satellite to aid the National Oceanic and Atmospheric Administration (or NOAA), which NASA calls "the lead agency on oil spills," as NOAA has been using plane fly-overs to monitor the situation.
So far, there really isn't any concrete strategy on how to plug up the damage done by the sinking rig. BP, the company which leased the Deepwater Horizon, has used underwater robots to no avail, and is even considering a massive deep-sea dome that would suck up the oil. You can check out the NASA link below to see the progression of the oil creep in satellite images.