A Department for Transport study has revealed some of the most congested trains in England are running at almost double capacity.
The government has called on train operators to do more to address overcrowding on rush-hour services.
In Autumn 2011, First Great Western's 07:44 Henley-on-Thames to London Paddington service had a 180% load factor in standard class carriages.
Watchdog Passenger Focus has called for greater investment in rolling stock.
Michael Roberts, chief executive of The Association of Operating Companies (ATOC), said overcrowding was the "flip side" to faster trains and better services.
In a statement he said train companies understood passengers' frustration and were "taking action where they can".
He said the government needed to give operators "more flexibility to respond to passenger demand".
'Long term investment'
Watchdog spokesman Mike Hewitson said: "Passengers tell us that getting a seat is a daily struggle.
"We need substantial long-term investment to provide longer and more frequent trains to help reduce crowding.
"The industry needs to increase capacity by offering more trains and more carriages - not by increasing fares to price off demand."
From 2 January, season ticket holders in Henley-on-Thames will also see their annual fare to London rise by 4.18% to £3,388.
First Great Western has recently added an extra carriage to the 07:44 service, increasing the number of standard class seats to 340.
Dan Panes, from the operator, said: "Over the last three years we have managed to deliver 90 more carriages across our network, pulling in an additional 10% capacity.
"This strategy has made a huge difference and it's important to remember these figures were collected more than a year ago.
"We're confident next year's data will show the difference our approach is making."
In the majority of the top 10 overcrowded trains, capacity is determined by the number of standard class seats only.
A standing allowance was factored in for the National Express East Anglia London Liverpool Street to Shenfield 18:17 train and London Midland's 07:55 Stourbridge Junction to Stratford-upon-Avon service.
London Midland, which features in the top 10 list four times, has placed an order for 10 new four-car trains which will allow for additional services to operate on the route from 2014.
Transport Minister Norman Baker said: "The operators on the list are aware of the problems on these services.
"I will be monitoring them closely, and others which have not made the top 10 list, urging train companies to reduce crowding on the busiest services."