Commuters crammed into rush-hour trains would probably consider their own service to be the most overcrowded in the country.
But the busiest route in terms of crowding is the 7.44am Henley-on-Thames to Paddington in London, according to new Government figures.
That train, taking people from the Oxfordshire town into the capital, a 40 mile journey, has a load factor of 180%.
This means that when the survey was carried out - during autumn 2011 - the Henley-London service was travelling 80% over capacity in standard-class carriages.
From January 2, Henley season ticket holders will see their annual fare rise 4.18% to £3,388.
Publishing the figures, the Department for Transport (DfT) said the First Great Western company had recently added an extra carriage to the 7.44am train, taking the number of standard-class seats to 340.
The second most crowded service was the 7.32am from Woking in Surrey to Waterloo in London, which was 64% over capacity.
Third and fourth were two evening services from Euston station in London to Birmingham New Street - the 6.13pm from Euston, which was 62% over capacity and the 4.48pm at 60% over capacity.
Fifth, at 58% over capacity, was the 6.30am Banbury in Oxfordshire to Paddington in London service, while in sixth place, at 57% over capacity, was the 7.55am train from Stourbridge Junction to Stratford-upon-Avon in the West Midlands.
In seventh place, at 55% over capacity, was the 6.23am from Manchester Airport to Middlesbrough, while in eighth position was the 6.17pm train from Liverpool Street in London to Shenfield in Essex, which was 54% over capacity.
At 52% over capacity, the 7.14am service from Alton in Hampshire to Waterloo was ninth, while the 10th most-crowded service was another London-Birmingham evening rush-hour service - the 5.46pm Euston to Birmingham New Street, which was 52% over capacity (rounded up but slightly lower than the ninth place figure).
Transport Minister Norman Baker said: "Climbing on a crowded train where there is little space can often be an unpleasant experience and I sympathise with passengers who have to travel on these services.
"The operators on the list are aware of the crowding problems on these particular services. I will be monitoring these services closely, and others which have not made the top 10 list, and urging train companies to reduce crowding on the busiest services."
The DfT said that from this month London Midland (LM) was providing three Class 350/2 "high density" units for the 6:13pm service from London to Birmingham New Street to maximise the number of seats.
In the long term, LM has 10 new four-car trains on order that will allow the company to operate additional trains on this route from 2014.
The department also said that from September 2012, the 6:30am Banbury-Paddington train has started from Oxford not Banbury, leaving Oxford at 7am. It is now operated by a different type of rolling stock which provides a higher standard-class seating capacity.
The DfT said more recent counts on the 7.55am Stourbridge Junction to Stratford-upon-Avon "suggest much lower loadings on this service".
In the long term, from the May 2014 timetable period, it is planned to introduce a fifth train per hour between Manchester and Leeds which should relieve capacity on the 6.23am from Manchester Airport to Middlesbrough.
Michael Roberts, chief executive of the Association of Train Operating Companies, said: "Faster trains and better services are attracting record numbers of people to the railways, but the flipside is overcrowding on some routes.
"Train companies understand passengers' frustration when they cannot get a seat and operators are taking action where they can."
Campaign for Better Transport's campaigns director, Richard Hebditch, said the latest statistics showed overcrowding continued to be a problem.
"Year after year, fares go up faster than wages yet many passengers find themselves having to stand in cramped conditions."
He went on: "Passengers are tired of politicians promising lower fares and better services sometime in the future. We need action now to stop commuters paying excessive fares and to cut the level of overcrowding."
These were the 10 most-crowded routes according to data collected in autumn 2011. The load factor figure is based on 100% being the normal capacity of the train:
OPERATOR SERVICE LOAD FACTOR
1. FGW 7.44am Henley-on-Thames to London Paddington 180%
2. SWT 7.32am Woking to London Waterloo 164%
3. LM 6.13pm London Euston to Birmingham New Street 162%
4. LM 4.48pm Euston to Birmingham New Street 160%
5. FGW 6:30am Banbury to Paddington 158%
6. LM 7.55am Stourbridge Junction to Stratford-upon-Avon 157%
7. FTP 6.23am Manchester Airport to Middlesbrough 155%
8. NE 6.17pm London Liverpool Street to Shenfield 154%
9. LM 7:14pm Alton to Waterloo 152%
10. LM 5.46pm Euston to Birmingham New Street 152%*
* Rounded-up figure but slightly lower than the ninth-placed Alton service.
The operator abbreviations are FGW - First Great Western; SWT - South West Trains; LM - London Midland; FTP - First TransPennine Express; NE - National Express East Anglia.