These generally require enhanced oil recovery techniques such as gas (CO2) injection, chemical injection, microbial injection, cyclic steaminjection, steam flooding, and fire flooding.
Because it can take months of steaminjection to bring the reservoir up to optimal temperatures, producers are loathe to halt the process for fear of damaging their sands and gumming up their gear.
It must either be mined from the surface like coal (to which it is just as similar as it is to oil) or through expensive steaminjection with or without the injection of petroleum distillates.