Across the league, clubs paid around a third above Transfermarkt valuations for players in the scramble to strengthen their squads.
So, to make fairer comparisons, we've adjusted those valuations for this summer's transfer inflation, and then measured which clubs bought below that benchmark and sold above it.
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It was a summer of high-profile exits for Aston Villa but they rank as the best buyers of the window according to our adjusted figures.
Our analysis shows Villa's signings had a collective value £60.0m higher than they paid. The biggest bargain was midfielder Johan Manzambi, who had an adjusted value of £74.8m at the time of his £47m move from Freiburg.
Leon Goretzka was brought in for free following the expiry of his contract at Bayern Munich but had an adjusted value of £13.8m, while Joao Gomes, Matteo Ruggeri and Zion Suzuki were also signed for fees much lower than their adjusted values.
Arsenal's attempts to add a blockbuster attacker ended in frustration but they rank as our second-best buyers, with Piero Hincapie, signed from Bayer Leverkusen for £34.5m with an adjusted value of £57.5m, one of the best-value additions of the window.
Christos Tzolis, Bruno Guimaraes and free transfer Illan Meslier also had adjusted values higher than the fees paid, giving Arsenal's signings a collective value £46.6m higher than their cost.
Chelsea's transfer policy has been criticised in recent years but the Blues come out as the third-best buyers of the window, with signings valued at £38.3m higher than their collective cost.
A large chunk of that value came from Valentin Barco, who had an adjusted value of £46.0m at the time of his £34m move from Strasbourg to Stamford Bridge, and, surprisingly, from £117m signing Morgan Rogers, who had an adjusted value of £126.6m, despite the perception that they overpaid for him.
At the other end of the scale, Newcastle rank as the worst buyers of the window in terms of finding value. Our analysis shows they overpaid for Aladji Bamba, a £35.5m signing from Monaco, to the tune of £14.8m. Matias Fernandez Pardo is also rated as a hefty overpay based on his adjusted value.
Liverpool come out as the second-worst buyers, largely because of the fees paid for Bradley Barcola and goalkeeper Lucca Brughmans, which came in at £19.4m and £25.4m above value respectively.
Spurs are next on the list. Curiously, they had both the best- and worst-value signings of the summer, according to our analysis.
Marcos Senesi arrived on a free transfer from Bournemouth with an adjusted value of £28.8m, making him the joint-best-value signing alongside Leeds' Harry Wilson. But the club paid a whopping £44.7m above value with their £85m deal for Savio, an overpay which was only partially mitigated by their other signings.
Who were the best and worst sellers?
Selling proved far more difficult for Premier League clubs overall, with Manchester City and Brentford the only sides in the division to emerge with positive efficiency scores for sales in our analysis.
Manchester City rank as the best sellers, having recouped £1.0m above the adjusted value of their players sold.
Their best sale was that of Savio, whose £85m move to Spurs came in £44.7m above his adjusted value, while James Trafford's £40m move to Leeds was £11.2m above value.
Brentford effectively broke even on their departures, finishing just £0.03m above the collective adjusted value of the players they sold.
Chelsea rank third, with their departure score just £0.5m below value overall.
Their best sale was that of Liam Delap, who joined Nottingham Forest for £17.8m more than his adjusted value at £50m, while the £125m sale of Enzo Fernandez to Manchester City on Deadline Day also came in at £9.9m above value.
On the flipside, our analysis suggests Chelsea sold defenders Trevoh Chalobah and Marc Cucurella for £15.2m and £17.2m less than their respective adjusted values, ensuring that the club's departure efficiency score was not as high as it might have been.
Our data for sales is grim reading for Liverpool, who rank as the worst sellers of the summer, with their fees received coming in at £95.9m below the collective value of the departing players.
This is largely because of losing Ibrahima Konate, a player with an adjusted transfer value of £51.8m, on a free transfer, along with Andrew Robertson, who had an adjusted value of £8.1m.
But the fees received for Mohamed Salah and Curtis Jones also fell well below their values, according to our analysis.
Spurs rank as second-worst sellers, having generated £62.0m less in fees than the collective value of the players sold, with Cristian Romero, Luka Vuskovic and Djed Spence let go for £23.5m, £19.0m and £16.0m below market value respectively.
And what about overall?
When combining signing efficiency and departure efficiency, Chelsea come out as the most efficient club of the summer in terms of finding and generating value in their purchases and sales.
Their window ended in frustration as a deal to sign Lamine Camara collapsed on Deadline Day, but their overall efficiency score of £37.7m puts them ahead of Aston Villa on £27.1m and Crystal Palace on £23.1m.
At the other end of the scale, Liverpool rank as the least efficient side of the transfer window, with an efficiency score of -£136.6m putting them below Spurs on -£81.3m and Newcastle on -£70.8m.
