due to additional R&D program investments such as programs associated with improvement of fuel efficiency, GenDrive unit performance and new product development such as on-road delivery trucks, drone applications, and increase in headcount.
Selling, general and administrative expenses. Selling, general and administrative expenses includes cash and non-cash compensation, benefits, amortization of intangible assets and related costs in support of our general corporate functions, including general management, finance and accounting, human resources, selling and marketing, information technology and legal services.
Selling, general and administrative expenses for the three months ended September 30, 2020, increased $3.9 million, or 37.3%, to $14.3 million from $10.4 million for the three months ended September 30, 2019. This increase was primarily related to acquisition and debt restructuring charges in addition to increases in salaries, employee bonuses, stock-based compensation and headcount.
Selling, general and administrative expenses for the nine months ended September 30, 2020, increased $13.6 million, or 40.8%, to $46.9 million from $33.4 million for the nine months ended September 30, 2019. This increase was primarily related to acquisition and debt restructuring charges in addition to increases in salaries, employee bonuses, stock-based compensation and headcount.
Interest and other expense, net. Interest and other expense, net consists of interest and other expenses related to our long-term debt, convertible senior notes, obligations under finance leases and our finance obligations, as well as foreign currency exchange losses, offset by interest and other income consisting primarily of interest earned on our cash and cash equivalents, restricted cash, foreign currency exchange gains and other income. Since September 30, 2019, the Company assumed approximately $170.0 million of additional long-term debt at 12% interest (which interest was reduced to 9.5% on May 6, 2020), issued a 7.5% Convertible Senior Note at 7.5% interest, issued $212.5 million convertible senior notes at 3.75% interest, and entered into additional sale/leaseback finance obligation arrangements.
Net interest and other expense for the three months ended September 30, 2020 increased $9.3 million, or 116.3%, as compared to the three months ended September 30, 2019. This increase was attributable to an increase in interest expense associated with the Company’s finance obligations, long-term debt and the issuance of the convertible senior note, as mentioned above.
Net interest and other expense for the nine months ended September 30, 2020 increased $17.8 million, or 73.8%, as compared to the nine months ended September 30, 2019. This increase was attributable to an increase in finance obligations, long-term debt and the issuance of the convertible senior note, as mentioned above.
Common Stock Warrant Liability
The Company accounts for common stock warrants as common stock warrant liability with changes in the fair value reflected in the unaudited interim condensed consolidated statement of operations as change in the fair value of common stock warrant liability.
All remaining common stock warrants were fully exercised in the fourth quarter of 2019. As such, there was no change in fair value as of September 30, 2020.
Contingent Consideration
In the second quarter of 2020 the Company recorded a provisional amount of $7.8 million in contingent consideration, related to the valuation of Giner ELX’s earnout payments that the sellers are eligible to receive. In the third quarter of 2020, the Company assessed the fair value of the contingent consideration to be $8.9 million. The $1.1 million change in fair value of the contingent consideration is reflected in the unaudited interim condensed consolidated statement of operations for the three and nine months ended September 30, 2020.