The 4-player rules are still valid, but:
Players must decide at the beginning of the game if they are going to use 4 or 3 neighborhoods (in which case neighborhood #4 will not be used). Using 3 neighborhoods will make the game more strained!
There are only three gems to win in each port (i.e. the three gems on each 'Ship' card; the large stone now only counts as one gem). The player holding a majority in a neighborhood now wins two gems; the second player wins one gem; the third player wins nothing.
To fill the market, you only use the two smaller gems on the 'Ship' card. These gems are placed on lines 2 and 3 of the market. Brokers cannot be placed on line 1 (which is like line 0 in the 4-player game).
This version is played like the 3-player game (but you have to play on three neighborhoods).
Furthermore: Each player takes the 11 brokers of their color, plus four brokers ('4', '2', 'T and '0') belonging to a third color, representing the neutral player. The score token of this neutral player is placed on the starting square next to the markers of both human players. The bet for the turn order is settled normally between the two human players who take the '1 ' and '2' Order Cards.
Each player places their two brokers as usual (one faceup, the other facedown), plus one neutral broker facedown. A neutral broker can be placed anywhere, but once it is on the board, no player can check its value.
After the broker placing phase, you start counting points. Here are a few modifications for this phase :
The neutral player wins all the ties in which it is involved (there is only one exception: the neutral player can still be beaten by a player who owns the 'Intriguer' card). If the neutral player wins the 'Prince' or 'King' cards, points are normally scored.
If the neutral player wins another card, it is discarded and the player immediately gets a gem instead. When it has to choose a gem color, the neutral player automatically takes the strongest color on the market. If several colors are tied, the leftmost gem is automatically taken (blue, then green, then yellow, then red).
When the neutral player wins a neighborhood, the two gems with the highest values on the market are chosen among those featured on the 'Ship' card. If a white gem is available, it is automatically chosen first and given the color of the most valuable gem on the market (or the leftmost one in case of draw).
If the neutral player has to alter the quotations on the market, priority is given to the colors it owns in the largest amounts. If two or more colors are on a par, the leftmost color is chosen.
At the end of the game, if the neutral player has no gem in one color, points are scored as if the player were in the third place for this color.
Note: If the players are skilled enough, they can raise the neutral player's 'level' by changing the value of the neutral brokers each of them places, to 4, 3, 1 and 0 (and even more, if they want to).