Prior to the development of new extraction methods, bitumen, or oil sands, was not considered part of the world's oil reserves.

The statement is - True.

Before the development of the new extraction methods, bitumen, and oil sands were not considered as part of the oil reserves in the world, and this was because in that time it was impossible to get an oil of sufficient quality with the already existing methods of extraction. Since people did not saw a practical and economically justified usage for them, they were not included into the world's oil reserves as such. This changed after the technology advanced and new extraction methods enabled that the bitumen, and oil sands can be used commercially, so nowadays they are considered as part of the oil reserves.