Rail fares are set to increase by an average of 4.2% in January.
Watchdog Passenger Focus said some rail season ticket holders will face fare rises of almost 6%.
It found an annual ticket from Canterbury in Kent to London will be going up from £4,588 to £4,860 - a 5.9% rise.
Those buying season tickets from Tonbridge to London will face a 5.2% rise from January 2, with the cost going up to £3,796.
Other above-average increases highlighted by the group include Northampton to London (up 4.7% to £4,980); Morpeth to Newcastle (Berlin: NCI.BE - news) -upon-Tyne (up 5.0% to £1,008) and Llanelli to Swansea (up 5.4% to £624).
However, it also found some season tickets are not rising as much, while others are actually going down.
The cost of a season ticket from Shenfield in Essex to London dips in price from £2,720 to £2,704, while an Ellesmere Port to Chester annual ticket will only be going up by 2.3% to £720.
Among other season tickets rising by less than 4.0% are Aylesbury to London (up 3.2%), Cambridge (BSE: CTE.BO - news) to London (up 3.8%), Tain to Inverness (up 3.8%) and Stirling to Glasgow (up 3.9%).
The rises could have been steeper but for an intervention by the Government to limit the regulated fare rise to RPI inflation (as of July 2012) plus 1%, rather than the planned RPI plus 3% increase.
Train companies have the flexibility to raise some season tickets above the 4.2% ceiling as long as the average increase on their trains is no more than 4.2%.
Passenger Focus said it appeared train companies were exercising restraint but added that the price rises will still feel steep in some places.
Chief executive Anthony Smith said: "Passengers will feel this pain. After years of above-inflation fare rises, fresh increases are piling pressure on already high fares. The Government and the rail industry must now work together to deliver on the welcome promise to get fare rises in line with inflation."
Regulated fares account for around 40% of total fares. Train companies can raise these by as much as they like. Details of all fare rises are expected in the next few days.
Manuel Cortes, leader of the TSSA rail union, said the fare hikes were "intolerable", while RMT general secretary Bob Crow described them as "a full-frontal assault on passengers in the name of profit".
Rail Minister Norman Baker said: "Family budgets are being squeezed, so that is why this Coalition Government has taken pro-active steps to cut the planned fare rises from 3% to 1% above inflation until 2014.
"This decision puts an average of £45 per year back into the pockets of over a quarter of a million annual season ticket holders. Many more holders of weekly and monthly season tickets could also see lower fare rises and some commuters could be over £100 better off.
"It is misleading to search for the highest increase and then imply that that represents the average, as some I am afraid will do. It's worth noting that some fares, such as the season ticket from Shenfield to London, are actually going down."