I  found this on LOTRO web page I thought it was intresting.

Fellowship experience point distribution

Each member in a fellowship receives experience for a defeated foe that is based on their own level plus a fellowship bonus, with the resulting bonus amount then divided by the number of members in the fellowship. Unlike in other MMOs, the level spread of a fellowship can be quite large without unduly penalizing any member of the fellowship. Also unlike in other MMOs, there is not a finite amount of experience that is somehow divided among the members; instead, each member is evaluated individually to determine their experience award. This means that no member of the fellowship receives a disproportionate share of the experience awards. For example, a level 15 member gains the same exact experience award for a given foe regardless of whether the other members in the party are higher or lower than level 15.

The fellowship bonus is based on the table below:

• 2 members = 18% bonus
• 3 people = 46% bonus
• 4 people = 62% bonus
• 5 people = 82% bonus
• 6 people = 116% bonus

To illustrate how fellowship experience is awarded, assume a fellowship comprising 4 members, so the bonus percentage is 62% (a modifier of 1.62). If your normal “solo” experience award for defeating a foe would be 100 points, you would instead receive 41 points for defeating it as part of a 4-member fellowship, as follows:

• (solo exp award * bonus modifer) / number of members = fellowship experience award
• (100 * 1.18) / 2 = 59 experience points.
• (100 * 1.46) / 3 = 49 experience points.
• (100 * 1.62) / 4 = 41 experience points.
• (100 * 1.82) / 5 = 36 experience points.
• (100 * 2.16) / 6 = 36 experience points.

[edit] Penalty for any member being too much higher level than a foe

If any one member in the group is high enough in level that the foe is gray to them, every other member of the group receives only 66% of their usual fellowship experience award. For example, if a level 11 and a level 36 are in a 2-member fellowship together and they defeat a level 12 foe, the level 11 player will receive only 20 experience points, not the usual 30 points they would normally receive.

A likely theory behind the reason for this penalty is that it is an attempt to make a common form of power-leveling somewhat unattractive, but still be lenient enough to enable an incredibly wide level spread in fellowships compared to many other MMOs where the level spread is much smaller and more restrictive.

[edit] Penalty for being “assisted” by other players

If any other player(s) outside of your fellowship “assists” with the defeat of the foe in any way, the final divisor that is applied to your bonus-adjusted experience is based on the total number of contributors to the fight. For more information, see Mechanics:”Assist” Exp Penalty.

[edit] Bonus exp provides a strong incentive to form ad hoc fellowships

There is a common misconception among newer LOTRO players that being in a fellowship reduces or “slows down” your experience rate, so it's not uncommon to see several players individually farming an area for quest or deed foes instead of banding together in ad hoc fellowships. Using the numbers in the fellowship experience example from the previous section, you might normally receive an experience award of 100 points for defeating a certain foe, but if you are in a 2-member fellowship you receive “only” 60 points. If you're in a 3-member fellowship, you receive only 48 points. With 4 members, your experience award falls to 43 points, and so on.

This seems like a losing proposition until you examine the fact that a larger fellowship can defeat foes more quickly and safely. In the most extreme case, if a 6-member fellowship can defeat 6 foes in the same span of time that it takes you to defeat 1 foe all by yourself, you have actually made two-and-a-half times as much experience in that span of time than you could have by yourself. For example, assume those foes are worth 100 “solo” experience points. (6 * (100 * 2.49)) / 6 = 249 experience points.