In 2018, an unusual situation developed with respect to production of natural gas in the Permian Basin of western Texas and New Mexico. A news article noted the following two facts:

i. “Shale drillers in the Permian Basin are producing vast amounts of [natural] gas as a byproduct of prospecting for oil.”

ii. Natural “gas prices in parts of the prolific region hovered near zero last month and some trades went negative, to as low as a negative 25 cents per million British thermal units.”

a. What does it mean for a price to be negative?

b. Why would firms drilling in the Permian Basin continue producing natural gas if they receive a zero or negative price for it?