I'm proud to say that for the first time in Eagle's history, we sold over 2 million tons of cement during the quarter.
Our Wallboard shipments were up 7% over the same quarter a year ago.
This is in an environment where national shipments were down about 5%.
In this regard, it's worth noting that this quarter, our net leverage declined by $150 million for March 31st and total liquidity improved to over $450 million at June 30th.
We still have more to executing the separation, which at this moment has been delayed by COVID uncertainties.
First quarter revenue was a record $428 million, an increase of 15% from the prior year.
Excluding the recently acquired businesses and the effects of the business we sold in northern California, revenue improved 2% from the prior year.
First quarter diluted earnings per share were $2.31, an improvement of 146%.
Excluding these and other non-routine items, first quarter adjusted earnings per share improved 39%.
Revenue in the sector increased 30%, driven primarily by the contribution from the recently acquired Kosmos Cement Business and a 7% increase in like-for-like cement sales volume.
Operating earnings improved 62%, again reflecting a contribution for Kosmos and improved sales volume as well as lower diesel prices in our concrete operations.
In addition, given the concerns around having contractors onsite during the COVID-19 pandemic, we adjusted the timing extents of our cement maintenance outages and delayed approximately $6 million of maintenance costs from the first quarter into the second and third.
Quarterly operating earnings in this sector declined 8% to $44 million, as improved Wallboard earnings were offset by higher recycled fiber costs and the inefficiencies of starting up the paper mill after the expansion project in March.
The earnings impact from start-up was approximately $2 million and by the end of the quarter, our operating efficiencies at the mill were much improved.
In the Oil and Gas Proppants sector, revenue was down 93% and we had an operating loss of $1 million.
During the first quarter, operating cash flow improved 88% to $95.3 million, reflecting strong earnings and disciplined working capital management.
Total capital spending improved or increased to $26 million, as we completed several projects initiated last year and purchased land in Oklahoma, which will provide our two Wallboard plants with over 20 million tons of additional shifts and reserves.
We continue to expect total capital spending in a range of $60 million to $70 million for fiscal 2021.
At June 30th, our net debt to cap ratio was 55% and we had a $199 million of the cash on hand.
Our net debt to EBITDA leverage ratio was 2.5 times and total liquidity at the end of the quarter was $459 million and we have no near-term debt maturities.

Summary:
We still have more to executing the separation, which at this moment has been delayed by COVID uncertainties.
First quarter revenue was a record $428 million, an increase of 15% from the prior year.
First quarter diluted earnings per share were $2.31, an improvement of 146%.