These discussions will be followed by a Q&A session and we expect the call to last about 60 minutes.
Revenue was $1.6 billion for the fourth quarter.
Fourth quarter adjusted EBITDA was $262 million, and fourth quarter adjusted earnings per share was $1.75.
For the full year, 2020 revenue was $6.3 billion, 2020 adjusted EBITDA was $810 million, and 2020 full year adjusted earnings per share was $5.11.
And finally, cash flow from operations for the year was $937 million a record level.
Considering the impacts of the pandemic on the oil and gas industries, we laid out a path to achieving an annual revenue target of $10 billion with double-digit margins.
One of our key highlights of 2020 and was our ability to grow non-oil and gas revenues by almost 12% and non-oil and gas adjusted EBITDA by over 40% despite the pandemic.
Our guidance that we provided today reflects continued diversification, as we expect our non-oil and gas business to grow approximately 20% in revenues and approximately 45% in EBITDA in 2021.
While we didn't lay out a time line for our $10 billion revenue target in the third quarter, the visibility within our end markets has continued to improve.
Included in today's 2021 guidance, revenue contribution for these two companies is about $300 million.
Our communication revenue for the quarter was $569 million.
EBITDA margins came in better-than-expected at 11.1% and were up 300 basis points year-over-year.
For the year, revenues were $2.5 billion and margins were 10.7%, a 270 basis point improvement over last year.
Comcast became MasTec's third largest customer in 2020 growing over 100% from 2019 and our T-Mobile business also grew significantly in 2020 with sequential growth in the fourth quarter of approximately 60%.
The rural digital opportunity fund or RDOF which is a follow-up to the Connect America Fund will provide $20 billion of funding over the next 10 years to build and connect gigabit broadband speeds in unserved rural areas.
Additionally in October of 2020, the FCC established the 5G fund for rural America which will provide up to $9 billion in funding over the next decade to bring 5G wireless broadband connectivity to rural America.
We entered the rural telecom space in 1997 through an acquisition and have been serving this customer base for nearly 25 years.
Moving to our Electrical transmission segment, revenue was $126 million versus $116 million in last year's fourth quarter.
Moving to our oil and gas pipeline segment, revenue was $600 million.
On our third quarter call, we forecasted a longer-term recurring revenue target of $1.5 million to $2 billion a year, assuming a continued depressed oil and gas market.
As a reminder, over the last three years, less than 10% of our revenues have come from oil pipelines with the majority of our business being tied to natural gas.
Moving to our Clean Energy and Infrastructure segment, revenue was $1.5 billion for the full year versus $1 billion in the prior year, a roughly 50% year-over-year increase.
More importantly, EBITDA margins for the year were 5.3%, a 140 basis point improvement over last year.
While George will cover 2021 guidance in detail, I'd like to highlight that our 2021 guidance reflects strong 24% revenue growth.
In summary, while fourth quarter 2020 revenue was slightly below our expectation at $1.63 billion, earnings margin exceeded our expectation with fourth quarter 2020 adjusted EBITDA at $262 million or 16% of revenue, a 370 basis point increase when compared to the fourth quarter of last year.
This capped a strong year for MasTec, despite the negative impact of the COVID-19 pandemic with annual 2020 adjusted EBITDA of $810 million and strong adjusted EBITDA margin rate of 12.8%, a 110 basis point improvement over last year.
With 2020 revenue growing approximately $470 million or 12% and, 2020 adjusted EBITDA for these segments increasing $90 million or 43% when compared to 2019.
We ended 2020 with a new record level of cash flow from operations of $937 million this allowed us to reduce our net debt levels during 2020 by $481 million to approximately $880 million which equates to a book leverage ratio of just over one.
Fourth quarter 2020 Communications segment revenue of $568 million decreased 16%, compared to the same period last year.
Fourth quarter 2020 Communications segment adjusted EBITDA margin rate exceeded our expectation at 11.1% of revenue, a strong 310 basis point improvement compared to the same period last year.
Annual 2020 Communications segment revenue was approximately $2.5 billion with an adjusted EBITDA, at $270 million or 10.7% of revenue.
Annual 2020 adjusted EBITDA for this segment increased $61 million or 29%.
And adjusted EBITDA margin rate grew 270 basis points, when compared to 2019.
Looking forward to 2021, we expect that annual Communications segment revenue will grow approaching a double-digit range and approximate $2.8 billion with continued 2021 adjusted EBITDA margin rate improvement approximating 75 basis points to 100 basis points over 2020 levels.
Fourth quarter 2020 clean energy and infrastructure or clean energy segment revenue was $345 million, generally in line with our expectation.
Annual 2020 clean energy revenue was $1.53 billion, an increase of $492 million or 48% compared to 2019.
Fourth quarter 2020 clean energy adjusted EBITDA was $11 million, or 3.2% of revenue and annual 2020 clean energy adjusted EBITDA was $80 million or 5.3% of revenue, generally in line with our expectation.
Fourth quarter 2020 adjusted EBITDA rate fell slightly below the annual 2020 rate of 5.3%, primarily due to fixed costs on seasonally lower fourth quarter revenue.
At 5.3% of revenue annual, 2020 Clean Energy adjusted EBITDA margin rate increased 140 basis points compared to 2019.
We anticipate that 2021 Clean Energy revenue will grow in the high 30% range and approach $2.1 billion in 2021, with continued 2021 adjusted EBITDA margin rate improvement of approximately 125 to 150 basis points over 2020 levels.
Fourth quarter 2020 oil and gas segment revenue was $600 million, a 30% sequential growth over the third quarter, representing the first 2020 quarterly period in which this segment exhibited revenue growth over 2019, as we initiated project activity on selected large projects that will extend into 2021.
Annual 2020 oil and gas segment revenue was approximately $1.8 billion, a decrease of $1.3 billion when compared to 2019, again due to regulatory delays in large project activity, as previously discussed.
Fourth quarter 2020 oil and gas adjusted EBITDA was $196 million or 33% of revenue and annual 2020 oil and gas adjusted EBITDA was $511 million, a $123 million decrease when compared to 2019.
We estimate that annual 2021 oil and gas segment revenue will grow in the 30% range and approach $2.4 billion, with virtually all this activity in backlog as of year-end 2020.
Fourth quarter 2020 electrical transmission segment revenue was $126 million, generally in line with our expectation.
And annual 2020 electrical transmission revenue was $506 million, a 22% increase over 2019.
Fourth quarter 2020 electrical transmission segment adjusted EBITDA margin rate was below our expectation at 0.6% of revenue, due to inefficiencies and delays on a project that is approximately 85% complete as of year-end 2020.
This project also impacted our annual 2020 electrical transmission segment adjusted EBITDA margin rate, which was 2.9% as compared to 7.1% in 2019.
Looking forward to 2021, we expect annual 2021 electrical transmission segment will show strong revenue growth, somewhere in the high-teens to low 20% range.
Now I will discuss a summary of our top 10 largest customers for the annual 2020 period as a percentage of revenue.
AT&T revenue derived from wireless and wireline fiber services was approximately 14% and installed to the home services was approximately 4%.
On a combined basis, these three separate service offerings totaled approximately 18% of our total revenue.
Comcast, NextEra Energy, Crimean Highway pipeline and energy transfer affiliates were each at 5% of revenue.
Verizon, Xcel Energy, Duke Energy, Iberdrola Group and Enbridge were each at 4% of revenue.
Individual construction projects comprised 64% of our annual revenue with master service agreements comprising 36% and highlighting that we have a significant portion of our revenue derived on a recurring basis.
At year end 2020, our backlog was approximately $7.9 billion, a slight sequential increase compared to $7.7 billion as of the 2020 third quarter and a slight decrease compared to $8 billion as of year end 2019.
For the year ended 2020, we generated a record level $937 million in cash flow from operations and ended the year with net debt of $880 million, which equates to a book leverage ratio of 1.1 times.
We ended 2020 with $423 million in cash on hand as well as record liquidity defined as cash plus borrowing availability of approximately $1.6 billion.
During 2020, we reduced our net debt levels by approximately $481 million while still investing approximately $170 million in share repurchases and strategic investments.
We ended 2020 with DSOs at 86 days down four days compared to 90 days last year and generally in line with our expected DSO range in the mid to high-80s.
Regarding our spending on equipment, annual 2020 net cash capex, defined as cash capex net of equipment disposals, was approximately $177 million and we incurred an additional $114 million in equipment purchase under finance leases.
We anticipate lower levels of capex spending in 2021 at approximately $100 million in net cash capex, with an additional $120 million to $140 million to be incurred under finance leases.
We are projecting annual 2021 revenue of $7.8 billion with adjusted EBITDA of $875 million or 11.2% of revenue and adjusted diluted earnings of $5 per share.
We expect annual 2021 interest expense levels to approximate $58 million with this level including approximately $110 million of first quarter 2021 acquisitions, while excluding any potential additional M&A, strategic investments or share repurchase activity that may occur over the balance of 2021.
We expect to maintain a strong cash flow profile in 2021 with free cash flow once again exceeding 2021 adjusted net income despite expected working capital requirements related to our planned 24% revenue growth in 2021.
For modeling purposes, our estimate for 2021 share count is 74 million shares.
We expect annual 2021 depreciation expense to approximate 4.2% of revenue inclusive of first quarter 2021 M&A activity and capital additions.
We expect annual 2021 corporate segment adjusted EBITDA to be a net cost of approximately 1.1% of overall revenue.
And lastly, we expect that annual 2021 adjusted income tax rate will approximate 25%.
Our first quarter 2021 revenue expectation is $1.65 billion with adjusted EBITDA of $172 million or 10.4% of revenue and earnings guidance at $0.80 per adjusted diluted share.
Notable first quarter 2021 expectations include segment revenue levels expected to generally approximate fourth quarter 2020 levels with first quarter 2021 oil and gas segment revenue expected to significantly grow and approximate $600 million due to expanded cost plus project activity.
In terms of some additional color on the expected timing of 2021 consolidated revenue performance, we expect first half 2021 consolidated revenue to grow at a mid-teens growth rate with second half 2021 consolidated revenue growth rate accelerating to the high 20% to low 30% range and our annual 2021 revenue growth expectation is 24% over the prior year.
Regarding our expected timing of 2021 consolidated adjusted EBITDA margin rate performance, we expect first half 2021 adjusted EBITDA margin rate will be in the high 10% range with second half 2021 adjusted EBIT margin rate in the high 11% range, with our annual adjusted EBITDA guidance at 11.2% of 2021 revenue.

Summary:
Revenue was $1.6 billion for the fourth quarter.
Fourth quarter adjusted EBITDA was $262 million, and fourth quarter adjusted earnings per share was $1.75.
We ended 2020 with $423 million in cash on hand as well as record liquidity defined as cash plus borrowing availability of approximately $1.6 billion.
We are projecting annual 2021 revenue of $7.8 billion with adjusted EBITDA of $875 million or 11.2% of revenue and adjusted diluted earnings of $5 per share.
Our first quarter 2021 revenue expectation is $1.65 billion with adjusted EBITDA of $172 million or 10.4% of revenue and earnings guidance at $0.80 per adjusted diluted share.