We expect the call to last about 60 minutes.
With over 2,000 team members, INTREN significantly expands our electric distribution and transmission capabilities and footprint.
With trailing 12-month revenues of approximately $550 million, and strong opportunities for future growth, we are very excited about our future opportunities.
The purchase price of approximately $420 million represents a purchase price multiple of roughly seven times without taking into account tax benefits that on a net present value basis, represent over a full multiple turn.
With approximately 900 employees across 31 states, Buyers brings new capabilities to MasTec that we've typically outsourced.
Revenue for the quarter was $1.775 billion.
Adjusted EBITDA was $204 million.
Adjusted earnings per share was $1.10.
Cash flow from operations was $257 million.
And backlog at quarter end was $7.9 billion.
Considering the pandemic challenges on the oil and gas industries, we laid out a path to achieving an annual revenue target of $10 billion with double-digit margins.
Our guidance that we provided today, including our most recent acquisition, reflects continued diversification as we expect, our non-Oil and Gas business to grow approximately 27% in revenues and over 40% in EBITDA in 2021, with significant acceleration in the second half of 2021.
Our communication revenue for the quarter was $568 million, and margins improved 70 basis points year-over-year.
Highlights for the quarter include our growth with T-Mobile, whose revenues increased fourfold over last year's first quarter, and for the first time, broke into our top 10 customer list.
Comcast revenues were also very strong in the quarter, increasing 61% from last year's first quarter.
That growth was offset with expected declines in both our Verizon and AT&T business, which were both down approximately 35%.
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 underserved rural areas.
Additionally, in October of 2020, the FCC established the 5G run -- fund for rural America, which will provide up to an additional $9 billion in funding over the next decade to bring 5G wireless broadband connectivity to rural America.
Revenue was $134 million versus $128 million in last year's first quarter.
Moving to our Oil and Gas pipeline segment, revenue was $726 million.
Last year, we forecasted a longer-term recurring revenue target of $1.5 to $2 billion a year, assuming a continued depressed oil and gas market.
As a reminder, over the last three years, only 6% of our revenues have come from oil pipelines with the majority of our business being tied to natural gas.
Revenue was $350 million for the first quarter versus $286 million in the prior year, a 22% year-over-year increase.
We expect full year's revenues to approximate $2.1 billion, a 37% increase over 2020.
Backlog was up sequentially by nearly $360 million.
And more importantly, subsequent to quarter end, we've already been awarded approximately $550 million of new projects.
We added nearly 2,000 new team members in this segment from the end of the first quarter in 2020 to the end of the first quarter in 2021.
In summary, we had strong first quarter results with record revenue of approximately $1.8 billion, a 25% increase over last year; record adjusted EBITDA of approximately $204 million, a 73% increase over last year; and record cash flow from operations of approximately $257 million, a 27% increase over last year.
First quarter results exceeded our expectation, with revenue exceeding expectation by approximately $125 million, adjusted EBITDA exceeding our expectation by approximately $32 million and adjusted diluted earnings per share exceeding expectation by $0.30.
We expect that $70 million of revenue and $20 million in adjusted EBITDA related to our first quarter beat, represents an increase to our annual 2021 view with the balance representing accelerated quarterly project timing within 2021.
We continued our strong cash flow performance during the first quarter, reducing our net debt levels by approximately $65 million to approximately $815 million, despite funding approximately $90 million in acquisitions during the quarter.
This equates to a book leverage ratio of less than one times, and we ended the first quarter with a record level of liquidity of approximately $1.7 billion.
First quarter Communications segment adjusted EBITDA margin rate was 8.6% of revenue, a 70 basis point improvement compared to the same period last year.
Our annual 2021 Communications segment expectation is that revenue will approximate $2.7 billion to $2.8 billion, with annual 2021 adjusted EBITDA margin rate improving 90 to 110 basis points over 2020 levels.
Clean Energy segment revenue was $350 million, and adjusted EBITDA was approximately $11 million or 3.1% of revenue.
We continue to expect annual 2021 Clean Energy segment revenue will grow in the high 30% range and approach $2.1 billion, with annual 2021 adjusted EBITDA margin rate improvement in the 70 to 110 basis point improvement over the prior year.
First quarter Oil and Gas segment revenue exceeded our expectation, with revenue at $726 million and adjusted EBITDA at $168 million.
We currently expect annual 2021 Oil and Gas segment revenue will range between $2.4 billion to $2.5 billion, with the continued expectation that annual 2021 adjusted EBITDA margin rate for this segment will be in the high teens range.
First quarter Electrical Transmission segment generally performed as expected, with revenue at $134 million and adjusted EBITDA margin rate at 2.7%, reflecting a seasonally slow quarterly revenue period, coupled with the continued impact of project inefficiencies discussed last quarter as we move toward project completion.
Looking forward to the balance of 2021, including the expected partial year operations of the INTREN acquisition, we expect annual 2021 revenue for the Electrical Transmission segment to approximate $950 million, and annual 2021 adjusted EBITDA margin rate to approximate 7.5% of revenue.
And this guidance includes approximately $330 million of revenue at a double-digit adjusted EBITDA margin rate for the recent acquisition of INTREN, which became effective in May 2021.
Now I'll discuss a summary of our top 10 largest customers for the first quarter period as a percentage of revenue.
Enbridge revenue was approximately 25%, comprised of Canadian Station and other project activity as well as a large project initiated during the first quarter that will resume in the latter part of the second quarter, once road frost bands are lifted.
AT&T revenue derived from wireless and wireline fiber services was approximately 8%, and install-to-the-home services was approximately 3%.
The on a combined basis, these three separate service offerings totaled approximately 11% of our total revenue.
NextEra Energy was 7%.
WhiteWater Midstream was 6%.
Verizon and Energy Transfer were each at 3%.
Nuke Energy, T-Mobile and Pattern Energy were each at 2% of revenue.
Individual construction projects comprised 72% of our first quarter revenue with master service agreements comprising 28%.
At March 31, 2021, our backlog was approximately $7.9 billion, essentially flat to $7.9 billion as of year-end 2020.
During the first quarter, we generated a record level, $257 million in cash flow from operations, and ended the quarter with net debt of $815 million, which equates to a book leverage ratio of 0.9 times adjusted EBITDA.
We ended the first quarter with DSOs at 80, just below our expected DSO range in the mid- to high 80s.
We ended the first quarter with $512 million in cash on hand as well as record liquidity defined as cash plus borrowing availability of approximately $1.7 billion.
During the first quarter, we reduced our net debt by $64 million despite approximately $90 million in first quarter acquisition funding.
During the second quarter of 2021, given the working capital associated with an expected $320 million increase in sequential quarterly revenue, coupled with the cash outflow for the INTREN acquisition, we expect that our leverage will temporarily increase during the quarter, while still maintaining substantial liquidity of approximately $1 billion, and comfortable leverage metrics within our target range.
As we look forward, past the second quarter to the balance of 2021, we expect continued strong cash flow generation despite the working capital associated with our planned 2021 revenue growth, with net debt at year-end, expected to reduce from second quarter levels and approximate $1.1 billion, leaving us with ample liquidity, and an expected book leverage ratio slightly over one times adjusted EBITDA.
We now project annual 2021 revenue of $8.2 billion with adjusted EBITDA of $930 million or 11.3% of revenue and adjusted diluted earnings of $5.40 per share.
This represents a $400 million increase in revenue guidance, a $55 million increase in adjusted EBITDA and a $0.40 increase in adjusted diluted earnings per share, comprised of the combination of our strong first quarter performance and the benefit of the INTREN acquisition.
We anticipate lower levels of net cash capex spending in 2021 at approximately $100 million with an additional $180 million to $200 million to be incurred under finance leases, and this expectation is inclusive of expected capital additions for first and second quarter acquisitions.
We continue to expect annual 2021 interest expense levels to approximate $58 million with this level, including over $500 million in first and second quarter 2021 M&A activity.
We expect to maintain a strong cash flow profile with annual 2021 free cash flow, once again exceeding adjusted net income, despite the working capital requirements related to our projected $1.9 billion increase in annual 2021 revenue.
For modeling purposes, our estimate for 2021 share count continues at 74 million shares.
We expect annual 2021 depreciation expense to approximate 4.1% of revenue inclusive of first and second quarter M&A activity.
Given these trends, we anticipate that next year, annual 2022 depreciation expense as a percentage of revenue will decrease when compared to 2021 levels and approximate 3.5% of revenue.
We expect annual 2021 Corporate segment adjusted EBITDA to be a net cost of approximately 1% of overall revenue.
Lastly, we expect that annual 2021 adjusted income tax rate will approximate 25%.
Our second quarter revenue expectation is $2.1 billion, with adjusted EBITDA of $229 million or 10.9% of revenue and earnings guidance at $1.25 per adjusted diluted share.
In terms of some additional color on the expected timing of second half 2021 revenue performance, we expect third quarter consolidated revenue growth in the mid- to high 30% range over the prior year, with third quarter 2021 consolidated adjusted EBITDA margin rate approximating 12% of revenue.

Summary:
We expect full year's revenues to approximate $2.1 billion, a 37% increase over 2020.
In summary, we had strong first quarter results with record revenue of approximately $1.8 billion, a 25% increase over last year; record adjusted EBITDA of approximately $204 million, a 73% increase over last year; and record cash flow from operations of approximately $257 million, a 27% increase over last year.
We continue to expect annual 2021 Clean Energy segment revenue will grow in the high 30% range and approach $2.1 billion, with annual 2021 adjusted EBITDA margin rate improvement in the 70 to 110 basis point improvement over the prior year.
We now project annual 2021 revenue of $8.2 billion with adjusted EBITDA of $930 million or 11.3% of revenue and adjusted diluted earnings of $5.40 per share.
Our second quarter revenue expectation is $2.1 billion, with adjusted EBITDA of $229 million or 10.9% of revenue and earnings guidance at $1.25 per adjusted diluted share.