completion activity steadily improved during the fourth quarter, albeit off a low base, ending the quarter up 67% sequentially in terms of the average frac spread count as reported by primary vision.
Our fourth-quarter results reflected 2% sequential growth in revenues and a significant 55% improvement in gross profits before DD&A, reflecting the cost mitigation measures implemented earlier in the year.
Partially offsetting these benefits was $2.7 million of severance and restructuring charges.
During the fourth quarter, our well site services revenues were up 3% sequentially, and adjusted segment EBITDA margins improved.
Our completion services incremental adjusted EBITDA margins came in at 89%.
In our downhole technologies segment, revenues continued their recovery and were up 24% sequentially, with adjusted segment EBITDA margins also up nicely.
In contrast, revenues in our offshore/manufactured products segment, which is a later-stage business, decreased 4% sequentially due primarily to weaker connector product sales.
Segment backlog at December 31, 2020, totaled $219 million, a decrease of 4% sequentially.
Our segment bookings totaled $65 million for the quarter, yielding what appears to be an industry-leading book-to-bill ratio of 0.9 times for the fourth quarter and 0.8 times for the year.
To that end, we had an exceptional year in 2020, generating $133 million of cash flow from operations.
With our significant free cash flow, we materially delevered during the year, reducing our total net debt by $128 million.
During the fourth quarter, we generated revenues of $137 million, while reporting a net loss of $19 million, or $0.31 per share.
Our revenues increased 2% sequentially, and our adjusted consolidated EBITDA improved significantly due to better cost absorption in our U.S. businesses.
For the fourth quarter of 2020, our net interest expense totaled $2.6 million, of which the majority are $1.8 million was noncash amortization of debt discount and debt issue costs.
At December 31, our net debt-to-book capitalization ratio was 12.8%, and our total net debt declined $128 million during 2020 through opportunistic open-market purchases of our convertible senior notes and repayments of borrowings outstanding under our revolving credit facility.
As Cindy mentioned, on February 10, we announced that we had entered into a new $125 million asset-based revolving credit agreement with a group of our key commercial relationship banks.
With a springing maturity 91 days prior to the maturity of any outstanding debt with a principal amount in excess of $17.5 million.
Borrowings outstanding under the new revolving credit facility will bear interest at LIBOR plus a margin of 2.75% to 3.25% based on our calculated availability under the facility with a LIBOR floor of 50 basis points.
We must also pay a quarterly commitment fee of 0.375% to 0.5% on the unused commitments.
At the closing of the new facility, we had approximately $29 million available, which was net of $12 million in outstanding borrowings and $29 million of standby letters of credit.
Together with $72 million of cash on hand at the end of December, pro forma liquidity would have been approximately $101 million.
At December 31, our net working capital, excluding cash and the current portion of debt and lease obligations, totaled $215 million.
In terms of our first-quarter 2021 consolidated guidance, we expect depreciation and amortization expense to total $23 million; net interest expense to total $2.1 million, of which approximately $1 million is noncash; and our corporate expenses are projected to total $8.4 million.
In this environment, we expect to invest approximately $15 million in total CAPEX during 2021, which is essentially flat when compared to 2020 spending levels.
In our offshore/manufactured products segment, we generated revenues of $76 million and adjusted segment EBITDA of $7.5 million during the fourth quarter.
Revenues decreased 4% sequentially due primarily to continued slow connector product sales.
Adjusted segment EBITDA margin of 10% compared to 12% margins achieved in the third quarter, reflecting lower revenues and reduced cost absorption.
As I mentioned earlier, orders booked in the fourth quarter totaled $65 million with a quarterly book-to-bill ratio of 0.9 times.
At December 31, our backlog totaled $219 million.
For over 75 years, our offshore/manufactured products segment has endeavored to develop leading-edge technologies, while cultivating the specific expertise required for working in highly technical, deepwater, and offshore environments.
While our 2020 bookings were lower than the levels achieved in 2019, our book-to-bill ratio for the year averaged 0.8 times, providing visibility as we progress into 2021.
In our downhole technologies segment, our revenues accelerated for the second quarter in a row, increasing 24%, while generating incremental adjusted segment EBITDA margins of 68% sequentially due primarily to cost savings measures implemented at the segment level.
Sales trends for our STRATX integrated gun systems and addressable switches continue to gain improved customer acceptance, and we experienced a 49% sequential improvement in international sales of our traditional perforating products.
In our well site services segment, we generated $39 million of revenue with sequentially increasing adjusted segment EBITDA.
Excluding the Northeast region, revenues increased 20% sequentially.
International and U.S. Gulf of Mexico market activity comprised 26% of our fourth-quarter completion service business revenues.
The fourth-quarter 2020 U.S. rig count average was 311 rigs, which was up 22% sequentially.
As we are now a month and a half into the first quarter of 2021, the average frac spread count has increased by about 26 spreads or roughly 20% since the fourth quarter.
We expect 2021 full-year consolidated EBITDA of $35 million to $40 million, with roughly 60% of the total generated in the second half of 2021.

Summary:
During the fourth quarter, we generated revenues of $137 million, while reporting a net loss of $19 million, or $0.31 per share.