Geographically, sequential growth in North America exceeded rig activity, growing in excess of 20% offshore and international revenue growth accelerated, closing the second half of 2021, up 12% versus the prior year.
All international areas posted growth, driven by gains in more than 75% of our international business units.
well construction and reservoir performance, our predominantly service-oriented Divisions, outperformed expectations with strong sequential growth and approximately 30% growth year over year on a pro forma basis.
And finally, we generated outstanding cash flow from operation exceeding $1.9 billion in the quarter.
At the end of 2021, we have more than 240 commercial DELFI customers, recorded more than 160% DELFI user growth year over year and saw a more than tenfold increase in compute-cycle intensity on our DELFI cloud platform.
We announced our comprehensive 2050 net-zero commitment, inclusive of Scope 3 emissions and launched the Transition Technologies portfolio to focus on the decarbonization of oil and gas operations with much success.
In essence, 2022 will be a period of stronger short-cycle activity resurgence driven by improved visibility in the demand recovery and greater confidence in the oil price environment.
And as oil demand exceeds prepandemic levels in 2023 and beyond, long cycle development will augment capital spending growth in response to the current supply.
Turning to 2022, more specifically, we expect an increase in capital spending of at least 20% in North America, impacting both the onshore and offshore markets, while internationally, capital spending is projected to increase in the low-to-mid teens, building momentum from a very strong exit in the second half of 2021.
In this scenario, increased activity and pricing will drive simultaneous double-digit growth both internationally and in North America that will lead our overall 2022 revenue growth to reach mid-teens.
Our ambition is to, once again, expand operating and EBITDA margins on a full year basis, exiting the year with EBITDA margins at least 200 bps higher than the fourth quarter of 2021.
This growth and margin expansion trajectory gives us further confidence that we will reach or exceed our mid-cycle ambition of 25% adjusted EBITDA margin before the end of 2023, leading to adjusted EBITDA that should visibly exceed 2019 levels in dollar terms.
Fourth quarter earnings per share excluding charges and credits was $0.41.
This represents an increase of $0.05 compared to the third quarter of this year and $0.19 when compared to the same period of last year.
In addition, we recorded a net credit of $0.01 bringing GAAP earnings per share to $0.42.
This consisted of a $0.02 gain relating to the sale of a portion of our shares in Liberty Oilfield Services, offset by a $0.01 loss relating to the early repayment of $1 billion of notes.
Overall, our fourth quarter revenue of $6.2 billion increased 6% sequentially.
All divisions posted sequential growth, led by digital and integration.
From a geographical perspective, International revenue grew 5%, while North America grew 13%.
Pretax operating margins improved 31 basis points sequentially to 15.8% and have increased for six quarters in a row.
Companywide adjusted EBITDA margin remained strong at 22.2%, which was essentially flat sequentially.
Fourth quarter digital and integration revenue of $889 million increased 10% sequentially with margins growing by 268 basis points to 37.7%.
Reservoir performance growth further accelerated in the fourth quarter with revenue increasing 8% sequentially to $1.3 billion.
Margins were essentially flat at 15.5% as a result of seasonality effects and technology mix, largely driven by the end of summer exploration campaigns in the Northern Hemisphere.
Well construction revenue of $2.4 billion increased 5% sequentially due to higher land and offshore drilling, both in North America and internationally.
Margins of 15.4% were essentially flat sequentially as the favorable combination of increased activity and pricing gains was offset by seasonal effects.
Finally, production systems revenue of $1.8 billion was up 5% sequentially, largely from new offshore projects and year-end sales.
However, margins decreased 85 basis points to 9%, largely as a result of the impact of delayed deliveries due to global supply and logistic constraints.
We delivered $1.9 billion of cash flow from operations and free cash flow of $1.3 billion during the quarter.
Cash flows were further enhanced by the sale of a portion of our shares in Liberty, generating net proceeds of $109 million during the quarter.
Following this transaction, we hold a 31% interest in Liberty.
On a full year basis, we generated $4.7 billion of cash flow from operations and $3 billion of free cash flow.
We generated more free cash in 2021 than in 2019, despite our revenue being 30% lower.
As a result of all of this, we ended the year with net debt of $11.1 billion.
This represents an improvement of $2.8 billion compared to the end of 2020.
During the year, we also continued to reduce gross debt by repaying $1 billion dollars of notes that were coming due in May of this year.
In total, our gross debt reduced by $2.7 billion in the last twelve months thereby significantly increasing our financial flexibility.
We expect total capital investments, consisting of capex and investments in APS and exploration data, to be approximately $1.9 to $2 billion dollars, as compared to just under $1.7 billion in 2021.
As a reminder, during the last growth cycle of 2009 to 2014 our total capital investment as a percentage of revenue was approximately 12%.

Summary:
In essence, 2022 will be a period of stronger short-cycle activity resurgence driven by improved visibility in the demand recovery and greater confidence in the oil price environment.
And as oil demand exceeds prepandemic levels in 2023 and beyond, long cycle development will augment capital spending growth in response to the current supply.
In this scenario, increased activity and pricing will drive simultaneous double-digit growth both internationally and in North America that will lead our overall 2022 revenue growth to reach mid-teens.
Fourth quarter earnings per share excluding charges and credits was $0.41.
Overall, our fourth quarter revenue of $6.2 billion increased 6% sequentially.
All divisions posted sequential growth, led by digital and integration.
From a geographical perspective, International revenue grew 5%, while North America grew 13%.
Pretax operating margins improved 31 basis points sequentially to 15.8% and have increased for six quarters in a row.
Reservoir performance growth further accelerated in the fourth quarter with revenue increasing 8% sequentially to $1.3 billion.
We expect total capital investments, consisting of capex and investments in APS and exploration data, to be approximately $1.9 to $2 billion dollars, as compared to just under $1.7 billion in 2021.