recent posts php troubles

on this page I added the php code below to try and get the post link title and a pic designated in a custom field (thumbpic) to show for all posts in category 18.

<h3>Supermarkets</h3>
<?php $recent = new WP_Query(); ?>
<?php $recent->query('cat=18'); ?>
<?php while($recent->have_posts()) : $recent->the_post(); ?>
<ul>
    <li>
            <a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
            <?php the_title(); ?>
            <?php $thumb = get_post_custom_values('thumbpic'); echo $thumb[0]; ?>
    </li>
</ul>
<?php endwhile; ?>

PHP:

The title and post link are working, but how come the pic from the custom field does not show????

please advise. thanks in advance.