I am attempting to query posts with different quantity of ID's which are contained in a wide array.

My array (known as $my_array) appears like this:

Array
(
    [0] => 108
    [1] => 129
    [2] => 145
)

And my Query appears like this:

<?php query_posts(array('post__in' => $my_array)); ?>

However this just returns one publish, the publish has got the ID from the first item within the array (108).

Have i got my syntax wrong?

$args = array(
  'post_type' => 'page',//or whatever type
  'post__in' => array(108,129,145)
  );
query_posts($args);

or

$arr=array(108,129,145);
$args = array(
  'post_type' => 'page',
  'post__in' => $arr
  );
query_posts($args);

A person always has to create the post_type using the post__in argument. So that your line need to look such as the following:

<?php query_posts(array('post_type' => 'post', 'post__in' => $my_array)); ?>

Which will query the posts using the IDs you've within the array.